Facile Preparation of Baclxfy for the Catalytic Dehydrochlorination of 1-Chloro-1,1-Diﬂuoroethane to Vinylidene Fluoride

catalysts

Article Facile Preparation of BaClxFy for the Catalytic Dehydrochlorination of 1-Chloro-1,1-Diﬂuoroethane to Vinylidene Fluoride

Wei Yu , Wenfeng Han * , Yongnan Liu, Jiaqin Lu, Hong Yang, Bing Liu, Haodong Tang, Aimin Chen and Ying Li

Industrial Institute of Catalysis, Zhejiang University of Technology, Hangzhou 310032, China; [email protected] (W.Y.); [email protected] (Y.L.); [email protected] (J.L.); [email protected] (H.Y.); [email protected] (B.L.); [email protected] (H.T.); [email protected] (A.C.); [email protected] (Y.L.) * Correspondence: [email protected]

Received: 28 February 2020; Accepted: 19 March 2020; Published: 1 April 2020

Abstract: BaClxFy as well as BaF2 and BaClF catalysts were prepared by solid-state reaction at room temperature with Ba(OH)2 as the precursor and NH4F/NH4Cl as the F and Cl sources. The catalysts were applied for the dehydrochlorination of 1-chloro-1,1-difluoroethane to vinylidene fluoride at 350 ◦C. The industrial manufacture of vinylidene fluoride (VDF) is carried out at 600–700 ◦C, whereas the BaClxFy catalysts provided a promising pathway to produce VDF at much lower temperatures. Unfortunately, the selectivity of VDF over BaF2 decreased from 94% to 84% along with the deactivation of the BaF2 catalyst monotonically. In the presence of small amounts of Cl in BaF2, stabilized selectivity was achieved. Over BaCl0.05F0.95, BaCl0.1F0.9 and BaCl0.25F0.75, no decrease in VDF selectivity was observed. Clearly, the presence of small amounts Cl during solid-state preparation inhibited the growth of BaF2 crystalline significantly. Far smaller particles were achieved. The particle size, or more precisely, the crystal size of the barium catalyst played a major role in the catalytic performance. In addition to the crystal growth, the presence of small amounts of Cl during catalyst preparation changed the chemical state of Ba, and therefore the adsorption and activation of the C–Cl bond for HCFC-142b were altered.

Keywords: barium chlorofluoride; catalytic pyrolysis; barium fluoride; dehydrochlorination; 1-chloro-1,1-difluoroethane; vinylidene fluoride

1. Introduction 1,1-difluoroethylene (VDF) is one of the major fluoromonomers, which are the feedstock for the production of various resins, rubbers membrane and paints [1]. The polymers derived from VDF (PVDF) or co-polymers with unique chemical resistance, stability at elevated temperatures, oxidation resistance, weatherability, piezoelectricity, dielectric and thermoelectricity, find wide applications in areas including petrochemical, electronic and electrical, and fluorocarbon coating [2]. VDF is the second largest product among fluorocarbons with an annual production capacity of above 53,000 tons. The demand for VDF is increasing rapidly. At present, in industry, VDF is usually produced via the dehydrochlorination of 1,1-difluoro-1-chloroethane (HCFC-142b) at reaction temperatures above 650 ◦C[3,4]. Dehydrochlorination is an efficient route for the preparation of 1, 1-dichloroethylene (VDC), vinyl chloride monomer (VCM), 2,3,3,3-tetrafluoropropene (HFO-1234yf), and ethylene oxychlorination [5–8]. As the dehydrochlorination of HCFC-142b is a highly endothermic reaction, very long reaction tubes are adopted to supply the reaction heat. Unfortunately, this also leads to the

Catalysts 2020, 10, 377; doi:10.3390/catal10040377 www.mdpi.com/journal/catalysts Catalysts 2020, 10, 377 2 of 13 generation of carbon deposition during the reaction process at elevated temperatures. Consequently, the reactor needs to be cut off to remove the coke after a period of reaction, which significantly reduces the efficiency of continuous production. We have reported that the dehydrochlorination of HCFC-142b is promoted by catalysts such as N-doped activated carbon [9], N-containing mesoporous carbon [10], and metal fluorides [3,4]. The presence of catalysts reduces the reaction temperature from 650 ◦C to lower than 350 ◦C, facilitating saving energy consumption and avoiding the formation of coke during reaction. Although N-doped activated carbon and mesoporous carbon materials exhibit a moderate conversion of HCFC-142b and high selectivity to VDF, they are difficult to recover following deactivation by coking. SrF2 shows a high activity for the pyrolysis of HCFC-142b to VDF under moderate conditions. However, its selectivity and stability are rather low [4]. Although the preparation of SrF2 microparticles with cubic structures improves the performance, the procedure is complicated and it is difficult to scale-up. Due to the formation of highly corrosive byproducts, HCl and HF, during pyrolysis of HCFC-142b, there are very rare choices for the exploration of proper materials as the catalysts. Therefore, carbon materials and metal fluorides which are HF-corrosion-resistant are the potential catalysts. In addition to carbon materials, metal fluorides were also systematically investigated for the catalytic pyrolysis of HCFC-142b [11]. Among the various metal fluorides, barium fluoride shows relatively high activity in this reaction, with selectivity to VDF of 95% [11]. Other metal fluorides, such as MgF2, AlF3 and fluorinated Cr2O3 were found to be catalysts for dehydrofluorination reactions [12–14]. Similar to the chlorination of AlF3 to aluminum chlorofluoride (ACF), BaF2 also tends to be chlorinated to BaClF by Cl species under reaction conditions [15]. Consequently, a rapid decrease in the conversion of HCFC-142b and selectivity to VDF was observed. In a similar reaction system for dehydrofluorination, which was catalyzed by AlF3, strong Lewis acid promoted both dehydrofluorination and coke deposition. As a result, a fast deactivation was seen. It was reported that the pre-deposition of carbon prior to reaction leads to the partial coverage of strong Lewis acid sites and improves the stability of catalysts [16]. As reported previously, BaF2 converts to BaClF via reaction with HCl at reaction temperatures, resulting in the deactivation of the catalyst [11,17]. Clearly, the inhibition of chlorination of the BaF2 catalyst by Cl species is one of the key challenges for the catalytic pyrolysis of HCFC-142b. In this study, barium fluoride was pre-chlorinated to barium chlorofluoride during the preparation of the catalyst. BaClxFy catalysts were prepared by solid-state reaction at room temperature with various molar ratios of Cl and F. The catalysts were applied for the pyrolysis of 1-chloro-1,1-difluoroethane to vinylidene fluoride. The effect of Cl composition on the performance of the BaF2 catalyst for catalytic pyrolysis was investigated.

2. Results The catalytic performance of barium chlorofluoride for the pyrolysis of 1-chloro-1,1-difluoroethane (CH3CClF2, HCFC-142b) to vinylidene fluoride (VDF, CH2=CF2) as a function of time-on-stream is shown in Figure1. The reactions were carried out at atmospheric pressure, a gas hourly space -1 velocity (GHSV) of 1200 h , and a reaction temperature of 350 ◦C. As expected, BaCl2 is rather inactive for the pyrolysis of HCFC-142b. However, consistent with our previous study, BaF2 is efficient for the promotion of pyrolysis [11]. In addition to VDF, vinylidene chlorofluoride (CH2=CClF, VCF) via dehydrofluorination was detected as the major carbon-containing by-product. As indicated in Figure1a, the conversion of HCFC-142b over BaClF is only around 10%, which is significantly lower than that of BaF2 (40%–60%). Hence, it is reasonable for the gradual deactivation of BaF2 catalysts following the chlorination to BaClF or BaCl2. Catalysts 2020, 10, x FOR PEER REVIEW 3 of 12

BaF2, stabilized selectivity is achieved. Over BaCl0.05F0.95, BaCl0.1F0.9 and BaCl0.25F0.75, no decrease in VDF selectivity is observed (Figure 1d). Although the activity is rather low, it is noted that VDF selectivity over BaClF is high and stable. All these differences are not attributed to the change in specific surface area. Determined by N2 adsorption and desorption, the specific surface areas of all catalyst samples are rather low (˂ 2 m2/g). We suggest that the specific surface play a minor role in Catalysts 2020, 10, 377 3 of 13 the performance difference of catalysts.

100 (a) BaF (b) BaCl F 2 40 0.025 0.975 BaCl F BaCl F 80 0.025 0.975 0.05 0.95 BaCl F 0.05 0.95 BaCl F 30 60 0.1 0.9 BaCl F 0.25 0.75

BaF 20 2 40 BaCl F 0.1 0.9 BaCl F 0.25 0.75 20 BaClF 10 BaClF Conversion Conversion of (%) HCFC-142b

BaCl Conversion of HCFC-142b (%) 2 0 0 0 4 8 12 16 20 24 18 20 22 24 Time on Stream (h) Time on Stream (h)

100 100 (c) (d) BaClF BaCl F 0.05 0.95 BaCl F 0.25 0.75 BaCl F 90 0.1 0.9

BaF 80 2

BaCl F 0.025 0.975 90 BaCl F 70 0.05 0.95 BaCl F 0.1 0.9 BaCl F 0.025 0.975 BaCl F 0.25 0.75 Selectivity to VDF (%) VDF to Selectivity Selectivity to VDF (%) VDF to Selectivity 60 BaClF BaF 2 BaCl2 50 80 0 4 8 12162024 18 20 22 24 Time on Stream (h) Time on Stream (h)

Figure 1. Catalytic performance of BaClxFy catalysts for the pyrolysis of HCFC-142b as a function of 1 timeFigure on stream 1. Catalytic at atmospheric performance pressure, of BaCl a gasxFy hourlycatalysts space for the velocity pyrolysis (GHSV) of HCFC-142b of 1200 h− , as and a afunction reaction of −1 temperaturetime on stream of 350 at ◦atmosphericC. (a) Conversion pressure, of HCFC-142b, a gas hourly (b space) Highlighted velocity conversion(GHSV) of 1200 of HCFC-142b h , and a reaction for the timetemperature on stream of between 350 °C. 14(a) and Conversion 24 h, (c) Selectivityof HCFC-142b, to vinylidene (b) Highlighted fluoride conversion (VDF) and of (d HCFC-142b) Highlighted for selectivitythe time toon VDF stream forthe between time on 14 stream and between24 h, (c) 14 Selectivity and 24 h. to vinylidene fluoride (VDF) and (d) Highlighted selectivity to VDF for the time on stream between 14 and 24 h. Different from the catalysts of BaF2, BaCl2 and BaClF, doping of small amounts of Cl to BaF2 formingAs BaCl arguedxFy changes previously, the conversion for both ofBaF HCFC-142b2 or BaClx slightly.Fy, the Comparedreason for withdeactivation BaF2, with during a doping the amountdehydrochlorination of less than 10%, reaction the conversion is that the levels catalyst are improved, reacts with while, the HCl with generated increased in amounts, the reaction, a similar and orthen even F lowerelements conversion on the resultscatalyst (Figure are further1b). replaced by Cl [11]. This is the major contributor to deactivation,Unexpectedly, in addition the doping to the of smallcoke deposition. amounts of ClClearly, to BaF both2 significantly BaClxFy and enhances BaF2 tend the selectivity to be further to VDFchlorinated (Figure1 c).during For the the BaF reaction.2 catalyst, However, the selectivity BaClxFy ofcatalysts VDF decreases exhibit an from improved 94% to 84%performance, along with while the deactivationBaF2 deactivated of BaF relatively2 catalyst monotonicallyrapidly. This may (Figure indicate1c). In that the the presence BaClxF ofy formed small amounts during preparation of Cl in BaF 2by, stabilizedsolid-state selectivity reaction isat achieved.room temperature Over BaCl is0.05 notF 0.95exactly, BaCl the0.1 sameF0.9 and as the BaCl BaCl0.25FxF0.75y formed, no decrease in the reaction, in VDF selectivityor after adding is observed Cl in the (Figure preparation,1d). Although it can significantly the activity is slow rather down low, the it is speed noted of that catalyst VDF chlorination selectivity overduring BaClF the is reaction. high and If stable. the catalyst All these is quickly differences chlorinated are not attributedto BaCl2, a todecrease the change in activity in specific is inevitable surface area.as the Determined BaCl2 phase by is N 2almostadsorption inactive. and Aluminum desorption, chlorofluoride the specific surface was areasconfirmed of all to catalyst be an samplesexcellent arecatalyst rather for low C-F (< bond2 m2 /activationg). We suggest and F/Cl that exchange the specific reaction surface [18,19]. play aSimilarly, minor role barium in the chlorofluorides performance diarefference proper of catalysts catalysts. for the dehydrochlorination of HCFC-142b. AsThe argued above previously,discussion is for confirmed both BaF by2 orthe BaClresultsxFy ,of the XRD. reason As indicated for deactivation in Figure during 2, BaF2 theand dehydrochlorinationBaClF phase structures reaction were is prepared that the by catalyst the simple reacts solid-state with the HCl reaction generated between in theBa(OH) reaction,2 and andNH then4F/NH F elements4Cl at room on temperature. the catalyst areThe further XRD patterns replaced of byBaF Cl2 and [11 ].BaClF This agree is the well major with contributor the standard to deactivation,patterns (ICSD-85-1341 in addition for to theBaF coke2 and deposition. ICSD-70-1183 Clearly, for BaClF). both BaCl No xotherFy and impurities BaF2 tend are to detected be further by chlorinated during the reaction. However, BaClxFy catalysts exhibit an improved performance, while BaF2 deactivated relatively rapidly. This may indicate that the BaClxFy formed during preparation by solid-state reaction at room temperature is not exactly the same as the BaClxFy formed in the reaction, or after adding Cl in the preparation, it can significantly slow down the speed of catalyst chlorination during the reaction. If the catalyst is quickly chlorinated to BaCl2, a decrease in activity is inevitable as the BaCl2 phase is almost inactive. Aluminum chlorofluoride was confirmed to be an excellent Catalysts 2020, 10, x FOR PEER REVIEW 4 of 12

XRD. Clearly, solid-state reaction at room temperature is an effective way for the synthesis of BaF2 and BaClF [20]. As disclosed in Figure 2a, BaF2 has a sharp diffraction peak indicating the complete crystallinity. Following the doping of small amounts of Cl, the crystallinity of BaF2 is weakened significantly. Catalysts 2020, 10, 377 4 of 13 Clearly, during preparation, in addition to the Cl source, the introduction of NH4Cl also functions as a template during the formation of BaF2 particles. Actually, during the process of low-temperature catalystsolid-state for synthesis, C-F bond activationboth the particle and F/ Clsize exchange and morphology reaction [ 18of ,solid19]. Similarly, products bariumcan be controlled chlorofluorides in the arepresence proper of catalysts proper fortemplates the dehydrochlorination [21–23]. A very weak of HCFC-142b. diffraction of BaClF is observed for BaCl0.1F0.9. WithThe the abovefurther discussion increase in is Cl confirmed content, bythe the XRD results pattern of XRD. gradually As indicated changes in from Figure BaF2,2 BaF to BaClF,2 and BaClFwhich phaseindicates structures that the were crystal prepared phase by of thethe simpleBaClF solid-stateis formed continuously reaction between after Ba(OH) adding2 andCl, which NH4F /isNH more4Cl atobvious room temperature.when the Cl content The XRD is higher patterns than of BaFthe 2BaCland0.25 BaClFF0.75, because agree well half with of the the BaF standard2 is transformed patterns (ICSD-85-1341into BaClF. In foraddition BaF2 and to the ICSD-70-1183 transformation for BaClF). of the No phase other structure, impurities the are 2θ detected of BaF2 byshifts XRD. following Clearly, solid-statethe addition reaction of Cl at (Figure room temperature 2b). Clearly, is an the eff ectivepresence way of for small the synthesis amounts of Cl BaF during2 and BaClF solid-state [20]. preparation disturbs the formation of BaF2 crystalline significantly [24,25].

ICSD-70-1183 (BaClF) (b) (101) ICSD-70-1183 (BaClF) (a) (002) BaClF BaClF (111) BaCl F BaCl F 0.25 0.75 0.25 0.75 BaCl F BaCl F 0.1 0.9 0.1 0.9 BaCl F BaCl F 0.05 0.95 0.05 0.95 Intensity (a.u.) Intensity(a.u.) BaF BaF 2 2

ICSD-85-1341 (BaF ) ICSD-85-1341 (BaF ) 2 2 10 20 30 40 50 60 23 24 25 26 2 Theta (°) 2 Theta (°)

FigureFigure 2.2.( a)(a XRD) XRD patterns patterns of BaF of2 andBaF barium2 and chloroﬂuoridebarium chlorofluoride catalysts beforecatalysts reactions. before ( breactions.) Highlighted (b) XRDHighlighted patterns XRD with patterns 2θ between with 23 2◦θand between 26◦. 23° and 26°.

AsThe disclosed changes inin Figurethe crystal2a, BaF structure2 has a sharpand surface diffraction of the peak catalysts indicating are further the complete reinforced crystallinity. by TEM Followingimages (Figure the doping 3). In ofthe small absence amounts of Cl, of lattice Cl, the diffraction crystallinity fringe of BaF (0.3622 is weakened nm) corresponding significantly. to Clearly,(111) of during preparation, in addition to the Cl source, the introduction of NH Cl also functions as a template BaF2 is detected [26]. In addition to BaF2, the BaClF crystal structure with4 a facet of (101), with a lattice during the formation of BaF particles. Actually, during the process of low-temperature solid-state diffraction fringe of 0.376 nm,2 corresponding to BaClF, is also found for BaCl0.25F0.75. Over BaClF, only synthesis,the lattice bothdiffraction the particle fringe size spacing and morphology of 0.376 nm of issolid identified, products indicating can be controlledthe exposure in the of presencethe (101) ofplane. proper This templates is consistent [21– 23with]. Athe very struct weakure dievolutionffraction revealed of BaClF in is XRD observed patterns. for BaCl 0.1F0.9. With the further increase in Cl content, the XRD pattern gradually changes from BaF2 to BaClF, which indicates that the crystal phase of the BaClF is formed continuously after adding Cl, which is more obvious when the Cl content is higher than the BaCl0.25F0.75, because half of the BaF2 is transformed into BaClF. In addition to the transformation of the phase structure, the 2θ of BaF2 shifts following the addition of Cl (Figure2b). Clearly, the presence of small amounts Cl during solid-state preparation disturbs the formation of BaF2 crystalline significantly [24,25]. The changes in the crystal structure and surface of the catalysts are further reinforced by TEM images (Figure3). In the absence of Cl, lattice di ffraction fringe (0.362 nm) corresponding to (111) of BaF2 is detected [26]. In addition to BaF2, the BaClF crystal structure with a facet of (101), with a lattice diffraction fringe of 0.376 nm, corresponding to BaClF, is also found for BaCl0.25F0.75. Over BaClF, only the lattice diffraction fringe spacing of 0.376 nm is identified, indicating the exposure of the (101) plane. This is consistent with the structure evolution revealed in XRD patterns.

Figure 3. High-resolution TEM images of (a) BaF2, (b) BaCl0.25F0.75.

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Figure 3. High-resolution TEM images of (a) BaF2, (b) BaCl0.25F0.75. Figure 3. High-resolution TEM images of (a) BaF2,(b) BaCl0.25F0.75.

Following reaction (time on stream of 24 h), no formation of BaCl2 was detected by XRD (Figure Following reaction (time on stream of 24 h), no formation of BaCl2 was detected by XRD (Figure S1). S1).By contrast, By contrast, the patternsthe patterns of spent of spent catalysts catalysts match ma withtch BaClFwith BaClF perfectly. perfectly. This indicates This indicates that the that BaClF the BaClF structure is relatively stable under reaction conditions (pyrolysis of HCFC-142b 350 °C) after structure is relatively stable under reaction conditions (pyrolysis of HCFC-142b 350 ◦C) after 24 hours 24of reaction.hours of Thisreaction. shows This that shows the deactivation that the deactivation rate was significantly rate was significantly slowed down slowed and the down selectivity and the to VDFselectivity was retained to VDF (Figurewas retained1). As BaClF(Figure phases 1). As are BaClF obtained phases for are all theobtained spent catalysts,for all the the spent same catalysts, activity theand same selectivity activity should and selectivity be achieved. should Actually, be achieved slight. Actually, differences slight in differences these catalysts in these are catalysts still noticed. are Therefore,still noticed. chlorination Therefore, ofchlorination catalysts is of not catalysts the sole is factornot the for sole the factor performance for the performance of catalysts. of catalysts. As shown in Figure 4, the contents of F and Cl of the BaClxFy catalyst before and after reaction As shown in Figure4, the contents of F and Cl of the BaCl xFy catalyst before and after reaction were obtained byby EDS.EDS. TheThe molarmolar ratio ratio of of F F/Cl/Cl after after reaction reaction and and the the calculated calculated ratio ratio of of chlorination chlorination of ofthe the catalyst catalyst after after reaction reaction are are related related to to the the amount amount of of Cl Cl addedadded duringduring the preparation of catalyst. catalyst. Clearly, the more Cl waswas added during the preparation,preparation, the less F in catalysts was chlorinated. After time on stream of 24 h, over 70% of F was replaced by Cl during the reaction for the BaF2 catalyst time on stream of 24 h, over 70% of F was replaced by Cl during the reaction for the BaF2 catalyst (Figure 4a). Although no diffraction peak of BaCl2 was detected by XRD over the spent catalysts, (Figure4a). Although no di ffraction peak of BaCl2 was detected by XRD over the spent catalysts, more more Cl than F was quantified by EDS over the spent BaF2 catalysts. As illustrated in Figure 4b, the Cl than F was quantified by EDS over the spent BaF2 catalysts. As illustrated in Figure4b, the ratio of ratio of F/Cl is lower than 0.4, implying the formation of BaCl2 species. We suggest that these BaCl2 F/Cl is lower than 0.4, implying the formation of BaCl2 species. We suggest that these BaCl2 structures structuresare highly are dispersed highly indispersed the catalyst. in the As catalyst. a result, As these a result, small these crystalline small particlescrystalline are particles not detected are not by XRD.detected It is by well XRD. accepted It is well that accepted the detection that the limit detecti of XRDon limit is 2–3 of nmXRD [27 is]. 2–3 Once nm again, [27]. Once the EDS again, results the EDSconfirm results that confirm BaClF is relativelythat BaClF stable is relatively under reaction stable under system. reaction Only small system. amounts Only of small F were amounts chlorinated of F wereduring chlorinated reaction. during reaction. With the doping of small amounts of Cl during the catalyst preparation, the chlorination of catalysts during the reaction is significantly inhibited. In addition to BaCl0.025F0.975, the catalysts are catalysts during the reaction is significantly inhibited. In addition to BaCl0.025F0.975, the catalysts are maintained at BaClF with an F/Cl of close to 1 (Figure 4b). Different from BaF2 catalyst, addition of maintained at BaClF with an F/Cl of close to 1 (Figure4b). Di fferent from BaF2 catalyst, addition of 4 2 NH4ClCl during during catalyst catalyst preparation prohibits the catalysts from being further chlorinated to BaClBaCl2 following reaction. As 80 presented in Figure1, BaClF exhibits rather low1.2 activity for the conversion of HCFC-142b, (a) (b) although70 it shows high selectivity to VDF. As BaCl F catalysts are ultimately chlorinated to BaClF, x y1.0 similar activities60 to BaClF should be obtained. However, much higher activities of these catalysts o were obtained (Figure1). Consequently, SEM experimentsi 0.8 were carried out for the elucidation of 50 these difference. ar rat ar 40 l 0.6 As displayed in Figure5, following solid-state reaction between Ba(OH) 2 and NH4F at room 30 mo temperature, irregular particles were obtained. The particle0.4 size ranges from 50 to 300 nm. Although F/Cl low-temperature20 solid-state reaction is an effective way to prepare nanomaterials, large BaF2 particles Chlorination degree (%) 0.2 were still10 formed, probably due to the fast fluorination of Ba(OH)2 by F ions [28]. However, with the doping of small amounts of NH4Cl, unexpectedly, much smaller and more uniform particles were 0 5 0.0 5 7 7 9 5 9 5 achieved for BaCl2 0.025F 0. F0.975.9 . Similarly,9 in.75 the presence of NaCl,2 ZnSF nanoparticles0. .9 9 with.75 a size ranging F 0 F 0. F 0 F F 0 F 0. F 0 F aF 5 aF 5 B 0 l .25 B 0 l .25 l 0.025 l 0.1 l 0 aCl l 0.025 l 0.1 l 0 aCl 0. C B 0. C B aC aC aC aC B B BaC Ba B B BaC Ba

Catalysts 2020, 10, x FOR PEER REVIEW 5 of 13

Figure 3. High-resolution TEM images of (a) BaF2, (b) BaCl0.25F0.75.

Following reaction (time on stream of 24 h), no formation of BaCl2 was detected by XRD (Figure S1). By contrast, the patterns of spent catalysts match with BaClF perfectly. This indicates that the BaClF structure is relatively stable under reaction conditions (pyrolysis of HCFC-142b 350 °C) after 24 hours of reaction. This shows that the deactivation rate was significantly slowed down and the selectivity to VDF was retained (Figure 1). As BaClF phases are obtained for all the spent catalysts, the same activity and selectivity should be achieved. Actually, slight differences in these catalysts are still noticed. Therefore, chlorination of catalysts is not the sole factor for the performance of catalysts. As shown in Figure 4, the contents of F and Cl of the BaClxFy catalyst before and after reaction were obtained by EDS. The molar ratio of F/Cl after reaction and the calculated ratio of chlorination of the catalyst after reaction are related to the amount of Cl added during the preparation of catalyst. Clearly, the more Cl was added during the preparation, the less F in catalysts was chlorinated. After time on stream of 24 h, over 70% of F was replaced by Cl during the reaction for the BaF2 catalyst (Figure 4a). Although no diffraction peak of BaCl2 was detected by XRD over the spent catalysts, more Cl than F was quantified by EDS over the spent BaF2 catalysts. As illustrated in Figure 4b, the ratio of F/Cl is lower than 0.4, implying the formation of BaCl2 species. We suggest that these BaCl2 structures are highly dispersed in the catalyst. As a result, these small crystalline particles are not detected by XRD. It is well accepted that the detection limit of XRD is 2–3 nm [27]. Once again, the EDSCatalysts results2020, 10confirm, 377 that BaClF is relatively stable under reaction system. Only small amounts6 of of 13F were chlorinated during reaction. With the doping of small amounts of Cl during the catalyst preparation, the chlorination of from 40 to 80 nm were prepared between the solid-state reaction of ZnCl2 and Na2S[29]. Clearly, catalystsCatalysts 2020 during, 10, x FORthe PEERreaction REVIEW is significantly inhibited. In addition to BaCl0.025F0.975, the catalysts6 ofare 13 both NH4Cl and NaCl can function as templates during the formation of particles via solid state maintainedreactions [30 at]. BaClF This result with is an consistent F/Cl of close with to the 1 observation(Figure 4b). ofDifferent XRD patterns. from BaF Following2 catalyst, the addition doping of of Figure 4. Chlorination of catalysts during the pyrolysis of HCFC-142b at 350 °C. (a) Chlorination NHCl, the4Cl crystalduring growthcatalyst of preparation BaF was inhibited prohibits signiﬁcantly. the catalysts from being further chlorinated to BaCl2 degree of catalysts after time2 on stream of 24 h. The chlorination degree is calculated according to the following reaction. molar ratio of F amount replaced by Cl in the reaction to the amount of F in the fresh catalysts. (b) 80 1.2 F/Cl molar(a) ratio in the spent catalysts. The elemental amounts(b) of all the catalysts were determined by 70 EDS technique. 1.0 60 o i 0.8 As50 presented in Figure 1, BaClF exhibits rather low activity for the conversion of HCFC-142b,

although it shows high selectivity to VDF. As BaClxFrat ar y catalysts are ultimately chlorinated to BaClF, 40 l 0.6 similar activities to BaClF should be obtained. However, much higher activities of these catalysts 30 mo were obtained (Figure 1). Consequently, SEM experiments0.4 were carried out for the elucidation of F/Cl these difference.20 Chlorination degree (%) 0.2 As10 displayed in Figure 5, following solid-state reaction between Ba(OH)2 and NH4F at room temperature, irregular particles were obtained. The particle size ranges from 50 to 300 nm. Although 0 5 0.0 5 7 7 9 5 9 5 2 F 0. .9 9 .75 2 F 0. .9 9 .75 2 low-temperature solid-stateF 0 reactiF 0. on Fis0 an effectiveF way to prepare nanomaterials,F 0 F 0. largeF 0 BaF F particles aF 5 aF 5 B 0 l .25 B 0 l .25 l 0.025 l 0.1 l 0 aCl l 0.025 l 0.1 l 0 aCl were still formed, probably0. due toC the fastB fluorination of Ba(OH)2 by F0. ions [28]. CHowever,B with the aC aC aC aC B B BaC Ba B B BaC Ba doping of small amounts of NH4Cl, unexpectedly, much smaller and more uniform particles were achieved for BaCl0.025F0.975. Similarly, in the presence of NaCl, ZnS nanoparticles with a size ranging Figure 4. Chlorination of catalysts during the pyrolysis of HCFC-142b at 350 ◦C. (a) Chlorination fromdegree 40 to 80 of nm catalysts were afterprepared time on between stream the of 24 solid-state h. The chlorination reaction of degree ZnCl is2 and calculated Na2S [29]. according Clearly, to both NH4theCl and molar NaCl ratio can of Ffunction amount replacedas templates by Cl during in the reactionthe formation to the amount of particles of F in via the solid fresh state catalysts. reactions [30].( bThis)F/Cl result molar is ratio consistent in the spent with catalysts. the observation The elemental of XRD amounts patterns. of all theFollowing catalysts the were doping determined of Cl, the crystalby EDSgrowth technique. of BaF2 was inhibited significantly.

Figure 5. SEM images of (a) BaF2, (b) BaCl0.025F0.975, (c) BaCl0.05F0.95, (d) BaCl0.1F0.9, (e) BaCl0.25F0.75 and (f) Figure 5. SEM images of (a) BaF2,(b) BaCl0.025F0.975,(c) BaCl0.05F0.95,(d) BaCl0.1F0.9,(e) BaCl0.25F0.75 andBaClF. (f) BaClF.

With the further doping of NH4Cl during catalyst preparation, a slight increase in particle size was observed. As presented in Figure 5, the particle size increases with Cl content monotonically. It is worth noting that very large particles for BaClF were obtained, with sizes ranging from 200 to 500

Catalysts 2020, 10, 377 7 of 13

CatalystsWith 2020 the, 10, furtherx FOR PEER doping REVIEW of NH4Cl during catalyst preparation, a slight increase in particle7 of size 13 was observed. As presented in Figure5, the particle size increases with Cl content monotonically. It is nm.worth Therefore, noting that the very particle large size particles of BaClF for BaClF is significantly were obtained, larger with than sizes that ranging of BaF from2 and 200 BaCl tox 500Fy. We nm. suggestTherefore, that the this particle mainly size contributes of BaClF to is significantlythe low activity larger of the than BaClF that ofcatalyst. BaF2 and BaClxFy. We suggest thatThe this mainlymorphology contributes of spent to thecatalysts low activity after a oftime the on BaClF stream catalyst. of 24 h is demonstrated in Figure S2. ComparedThe morphology with the SEM of spentimages catalysts of fresh after catalysts a time (Figure on stream 5), ofclear 24 hsintering is demonstrated is noticed in for Figure all the S2. catalysts.Compared Despite withthe the SEM formation images of of BaClF fresh after catalysts reaction, (Figure the5 ),particle clear sintering size of the is noticedcatalyst foris still all thefar smallercatalysts. than Despite that of the BaClF formation and the of BaClFspent afterBaClF. reaction, Hence, the the particle activity size of ofthe the BaCl catalystxFy catalysts is still far with smaller low Clthan content that of is BaClF still much and thehigher spent than BaClF. that Hence, of the theBaClF activity after ofreaction. the BaCl xFy catalysts with low Cl content is stillTo much verify higher the effect than of that crystal of the size BaClF on the after cataly reaction.tic performance, BaClF catalysts were calcined at 300, 400,To verify500 and the 600 eff ect°C ofin air crystal atmosphere. size on the Generally, catalytic metal performance, fluorides BaClFtend to catalysts sinter significantly were calcined at elevatedat 300, 400, temperatures 500 and 600 [31,32].◦C in airHence, atmosphere. in the pres Generally,ent study, metal BaClF fluorides catalysts tend were to sinter calcined significantly at high temperaturesat elevated temperatures to obtain various [31,32 crystal]. Hence, sizes. in theInterestin presentgly, study, as illustrated BaClF catalysts in Figure were 6, the calcined diffraction at high of BaClFtemperatures first decreases to obtain with various calcination crystal temperature sizes. Interestingly, followed as illustratedby increasing in Figureagain 6at, the temperatures di ffraction aboveof BaClF 400 first°C. Consequently, decreases with the calcination crystal sizes temperature were determined followed by by the increasing Scherrer equation again at temperaturesbased on the XRDabove patterns 400 ◦C. [33,34]. Consequently, Prior to the the crystal calcination, sizes were the crystal determined size of by BaClF the Scherrer was estimated equation to based be around on the 130.5XRD nm. patterns Following [33,34 ].calcination Prior to the at 300 calcination, °C, the size the decreases crystal size to of71.5 BaClF nm. wasFollowing estimated further to be increases around in130.5 temperature, nm. Following the sizes calcination of 52, 74 at and 300 ◦83C, nm the were size decreases obtainedto for 71.5 calcination nm. Following temperatures further increasesof 400, 500 in andtemperature, 600 °C respectively. the sizes of 52,Clearly, 74 and relatively 83 nm were low obtained calcination for calcinationtemperatures temperatures facilitate the of 400,disorder 500 and of BaClF600 ◦C structures. respectively. As Clearly,suggested relatively by Kesavamoorthy low calcination et al., temperatures the interplanar facilitate distance the of disorder Ba and F of planes BaClF dropsstructures. with Astemperature. suggested byBy Kesavamoorthycontrast, the Ba et and al., theCl plane interplanar is enhanced distance by of elevated Ba and Ftemperatures planes drops [35,36].with temperature. Nevertheless, By varied contrast, crystal the Ba sizes and Clof planeBaClF iswere enhanced achieved by elevated via calcination temperatures at different [35,36]. temperatures.Nevertheless, varied crystal sizes of BaClF were achieved via calcination at different temperatures.

BaClF-600

BaClF-500 BaClF-400

BaClF-300 Intensity (a.u.) Intensity BaClF

BaClF-Standard

10 20 30 40 50 60 70 80 2 Theta / °

FigureFigure 6. 6. XRDXRD patterns patterns BaClF BaClF catalysts catalysts calcined calcined at at temperatures temperatures between between 300 300 °C◦C and and 600 600 °C.◦C. Following XRD experiments, the calcined BaClF catalysts were further evaluated for the catalytic Following XRD experiments, the calcined BaClF catalysts were further evaluated for the catalytic pyrolysis of HCFC-142b. The results are displayed in Figure7. After calcination, the conversion levels pyrolysis of HCFC-142b. The results are displayed in Figure 7. After calcination, the conversion levels of HCFC-142b over BaClF are signiﬁcantly improved (Figure7a). Generally, the conversion agrees of HCFC-142b over BaClF are significantly improved (Figure 7a). Generally, the conversion agrees with the crystal sizes obtained by XRD patterns. BaClF calcined at 400 C exhibits a relatively high with the crystal sizes obtained by XRD patterns. BaClF calcined at 400 °C◦ exhibits a relatively high conversion with a small crystal size. Further increases in calcination temperature lead to the sintering conversion with a small crystal size. Further increases in calcination temperature lead to the sintering of BaClF. Correspondingly, the conversion drops with temperature. As small crystalline particles were of BaClF. Correspondingly, the conversion drops with temperature. As small crystalline particles obtained following calcination, stable selectivity to VDF is also achieved (Figure7b). were obtained following calcination, stable selectivity to VDF is also achieved (Figure 7b).

Catalysts 2020, 10, 377 8 of 13 Catalysts 2020, 10, x FOR PEER REVIEW 8 of 13

50 100 (a) (b) BaClF-400 40 90

BaClF-500 80 30 BaClF-300 70 BaClF-Air-600 20 BaClF-Air-500 60 BaClF-Air-400 BaClF-600 BaClF-Air-300 10 BaClF (%) VDF to Selectivity 50 BaClF-Original Conversion of HCFC-142b (%) 0 40 012345678 012345678 Time on Stream (h) Time on Stream (h)

FigureFigure 7. 7. EEffectﬀect of calcination calcination on on the the conversion conversion of (a of) HCFC-142b (a) HCFC-142b and (b and) selectivity (b) selectivity to VDF for to BaClF VDF for BaClFcatalysts. catalysts.

InIn comparison, comparison, BaF BaF22catalysts catalysts werewere also calcined under under the the same same temperatures. temperatures. As As disclosed disclosed in in FigureFigure S3a, S3a, di differentfferent from from BaClF, BaClF, a a strengtheningstrengthening in the diffraction diffraction of of BaF BaF2 2isis observed observed at atcalcination calcination betweenbetween 300 300 and and 600 600◦C. °C. According According to to the the calculation, calculation, the the crystal crystal size size of of BaF BaF2 increases2 increases from from 42 42 to to 51 51 and 55and nm after55 nm calcination after calcination at 400 and at 400 600 and◦C respectively. 600 °C respectively. Although Although these catalysts these catalysts were finally were chlorinated finally tochlorinated BaClF after to reaction BaClF after (Figure reaction S3b), (Figure they stillS3b), show they distillfferent show catalyticdifferent performances.catalytic performances. As shown As in Figureshown S4a, in Figure the calcination S4a, the calcination of BaF2 leads of BaF to2 leads a significant to a significant decrease decrease in the in conversionthe conversion of HCFC-142b.of HCFC- 142b. When calcined at 700 °C, BaF2 is almost totally deactivated. However, no clear difference was When calcined at 700 ◦C, BaF2 is almost totally deactivated. However, no clear difference was found forfound VDF for selectivity VDF selectivity (Figure (Figure S4b). S4b). BasedBased on on the the above above discussion, discussion, XRDXRD revealed that that a a smaller smaller crystal crystal size size was was achieved achieved following following ClCl doping doping (Figure (Figure2). 2). In In addition, addition, as as confirmedconfirmed by SEM images (Figure (Figure 5),5), Cl Cl doping doping also also lead lead to to the the decrease in the particle size. Hence, we suggest that the particle size or crystal size of a barium catalyst decrease in the particle size. Hence, we suggest that the particle size or crystal size of a barium catalyst plays a major role in the catalytic performance. Similar results were also confirmed for Cr2O3 catalysts plays a major role in the catalytic performance. Similar results were also confirmed for Cr O catalysts for the dehydrofluorination of 1,1-difluoroethane [37]. 2 3 for the dehydrofluorination of 1,1-difluoroethane [37]. The catalysts were further investigated by XPS characterization and the results are shown in The catalysts were further investigated by XPS characterization and the results are shown in Figure 8. The binding energy of Ba in BaF2 was determined to be 795.2 eV, which is consistent with Figure8. The binding energy of Ba in BaF was determined to be 795.2 eV, which is consistent with the the standard [38,39]. Upon the addition of2 Cl element to BaF2, a clear shift in Ba 3d3/2 towards a higher standard [38,39]. Upon the addition of Cl element to BaF , a clear shift in Ba 3d towards a higher binding energy is noticed (Figure 8a). Clearly, small amounts2 of Cl in BaF2 not only 3inhibit/2 the growth bindingof BaF2 energy and BaClF is noticed crystalline, (Figure but8 a).also Clearly, affect the small chemic amountsal state of of Cl the in Ba BaF element.2 not only Due inhibit to the different the growth ofinteractions BaF2 and BaClF of Ba crystalline,with Cl and but F, the also fast aff ectgrowth the chemical of crystalline state is of inhibited. the Ba element. In addition Due to to the the crystal different interactionsgrowth, these of Badifferences with Cl andmay F,also the contribute fast growth to th ofe crystallineimproved conversion is inhibited. and In selectivity. addition toDue the to crystal the growth,change these in Ba-binding differences energy, may also the contributeadsorption toand the activation improved of conversion the C-Cl bond and selectivity.for HCFC-142b Due are tothe changealtered. in Ba-bindingA similar trend energy, is also the adsorptionfound for the and F activation1s spectrum of the(Figure C-Cl 8b). bond Consistent for HCFC-142b with XRD are altered.and ATEM similar results, trend the is also XPS found spectra for of the spent F 1s catalysts spectrum confirm (Figure the8b). formation Consistent of BaClF with XRDduring and the TEM catalytic results, thepyrolysis XPS spectra of HCFC-142b of spent (Figure catalysts S5). confirm In addition the formationto the composition of BaClF of duringcatalysts, the reaction catalytic temperature pyrolysis of HCFC-142b[40], reaction (Figure pressure S5). and In addition environment to the [41] composition play an important of catalysts, role reaction in the catalytic temperature performance [40], reaction of pressurethe pyrolysis and environment process. These [41 issues] play will an importantbe addresse roled in inthe the future catalytic studies performance after the optimization of the pyrolysis of process.the catalysts. These issues will be addressed in the future studies after the optimization of the catalysts.

Catalysts 2020, 10, 377 9 of 13 Catalysts 2020, 10, x FOR PEER REVIEW 9 of 13

(a) BaCl -F (b) 2 BaClF BaClF BaCl F 0.25 0.75 BaCl F 0.25 0.75 BaCl F 0.1 0.9 BaCl F 0.1 0.9

BaCl F BaCl F 0.05 0.95 0.05 0.95 Intensity (a.u.) Intensity

Intensity (a.u.) BaCl F BaCl F 0.025 0.975 0.025 0.975

BaF BaF 3d 2 3d 2 3/2 5/2 805 800 795 790 785 780 775 690 688 686 684 682 680 678 Binding Energy (eV) Binding Energy (eV)

Figure 8. High resolution XPS of ( a) Ba 3d and ((b)) FF 1s1s spectraspectra ofof BaFBaF22 and barium chlorofluoridechlorofluoride catalysts before reactions. 3. Materials and Methods 3. Materials and Methods 3.1. Preparation of Catalysts 3.1. Preparation of Catalysts Barium chlorofluoride was synthesized by solid-state grinding method with the reaction between Barium chlorofluoride was synthesized by solid-state grinding method with the reaction Ba(OH)2 8H2O, NH4F and NH4Cl [42,43]. Ba(OH)2 8H2O, NH4F and NH4Cl were purchased from between ·Ba(OH)2·8H2O, NH4F and NH4Cl [42,43]. Ba(OH)· 2·8H2O, NH4F and NH4Cl were purchased Aladdin Co. (Shanghai, China) with analytical purity (>98.0%) without further purification. During from Aladdin Co. (Shanghai, China) with analytical purity (>98.0%) without further purification. the preparation of barium chlorofluoride, a total of 0.1mol NH4F and NH4Cl with different proportions During the preparation of barium chlorofluoride, a total of 0.1mol NH4F and NH4Cl with different were mixed and grinded in a mortar rigorously for 0.5 h. Then, 0.1 mol Ba(OH)2 8H2O powder was proportions were mixed and grinded in a mortar rigorously for 0.5 h. Then, 0.1 ·mol Ba(OH)2·8H2O added to the mixture, followed by grinding for a further 1 h. During the grinding, pungent gas was powder was added to the mixture, followed by grinding for a further 1 h. During the grinding, smelt (emission of NH3). Following the release of crystal water, wet paste was formed gradually. pungent gas was smelt (emission of NH3). Following the release of crystal water, wet paste was The paste was dried at 120 ◦C for 5 h, leading to the formation of barium chlorofluoride. For comparison, formed gradually. The paste was dried at 120 °C for 5 h, leading to the formation of barium neat BaF2 and BaCl2 were also prepared following similar procedures. The chemical equation used chlorofluoride. For comparison, neat BaF2 and BaCl2 were also prepared following similar during preparation is as follows. The conditions of catalyst preparation are listed in Table1. procedures. The chemical equation used during preparation is as follows. The conditions of catalyst preparation are listed in Table 1. Ba(OH)2 8H2O + NH4F + NH4Cl BaClxFy+NH3 +H2O BaሺOHሻ·2·8H2O + NH4F + NH4Cl →→ BaClxFy + NH3↑↑+ H2O

Table 1.1. Preparation conditionsconditions ofof catalystscatalysts forfor BaFBaF22, barium chloroﬂuoridechlorofluoride andand BaClBaCl22.

Amounts,Amounts, mol mol Catalyst Catalyst Ba(OH)2·8H2O NH4F NH4Cl Ba(OH)2 8H2O NH4F NH4Cl · BaF2 0.1 0.2 0 BaF2 0.1 0.2 0 BaCl0.05F1.95 0.1 0.195 0.005 BaCl0.05F1.95 0.1 0.195 0.005 BaCl0.1F1.9 BaCl0.1F1.9 0.1 0.190.19 0.01 0.01 BaCl0.2F1.8 BaCl0.2F1.8 0.1 0.180.18 0.02 0.02 BaCl F 0.1 0.15 0.05 BaCl0.5F1.5 0.5 1.5 0.1 0.15 0.05 BaClF 0.1 0.1 0.1 BaClF 0.1 0.1 0.1 BaCl2 0.1 0 0.2 BaCl2 0.1 0 0.2

3.2. Catalytic Activity 3.2. Catalytic Activity The catalytic activity of BaClxFy was evaluated in a tubular fixed-bed reactor. A nickel tube with The catalytic activity of BaClxFy was evaluated in a tubular fixed-bed reactor. A nickel tube with an inner diameter of 22 mm was adopted as the reactor. Blank experiments confirmed that no reaction an inner diameter of 22 mm was adopted as the reactor. Blank experiments confirmed that no reaction was detected in the absence of catalysts. The HCFC-142b (>99.0%, Juhua Co., Zhejiang, China) reaction was detected in the absence of catalysts. The HCFC-142b (>99.0%, Juhua Co., Zhejiang, China) gas was diluted by equivalent amounts of N2 (>99.9%, Mingxin Gas Co., Hangzhou, China) which reaction gas was diluted by equivalent amounts of N2 (>99.9%, Mingxin Gas Co., Hangzhou, China) were controlled by mass flow rate controllers (D09-11C, Qixing, Beijing, China) respectively. Prior to which were controlled by mass flow rate controllers (D09-11C, Qixing, Beijing, China) respectively. Prior to reaction, a 2 mL catalyst with a particle size ranging from 0.425 to 0.850 mm (20–40 mesh) was loaded to the isothermal zone of the reactor. A thermal couple was located in the middle the

Catalysts 2020, 10, 377 10 of 13 reaction, a 2 mL catalyst with a particle size ranging from 0.425 to 0.850 mm (20–40 mesh) was loaded to the isothermal zone of the reactor. A thermal couple was located in the middle the catalyst bed for the detection of reaction temperature. The reactions were carried out at atmospheric pressure, a gas 1 hourly space velocity (GHSV) of 1200 h− (HCFC-142b and N2), and a reaction temperature of 350 ◦C. KOH solution with a concentration of 1 mol/L was used to remove the eﬄuent acid gas (HCl and HF) formed during the reaction. A gas chromatograph (GC-1690 JieDao) equipped with a thermal conductivity detector (TCD) was used to analyze the gas composition.

3.3. Catalyst Characterization X-ray diffraction (XRD) experiments were carried out for the identification of crystal structures. XRD patterns were obtained over an X’Pert Pro analytical instrument (Almelo, Overijssel, The Netherlands). X-Ray photoelectron spectroscopy (XPS) measurements were performed by Thermo EscaLab 250Xi (Cambridge, Massachusetts, USA), equipped with monochromatized Al Kα X-ray as the excitation source (24.2 W). The binding energy values were corrected for charging effect by referring to the adventitious C1s line at 284.5 eV. Scanning electron microscopy (SEM) studies were carried out on a Helios G4 CX (Cambridg, Massachusetts, USA) equipped with an X-ray energy spectrometer (EDS). Transmission Electron Microscope (TEM) studies were carried out on a Tecnai G2 F30 (Hillsboro, Oregon, USA).

4. Conclusions

BaF2 and BaClxFy catalysts were successfully prepared via the solid-state reaction method at room temperature. Both catalysts promote the pyrolysis of HCFC-142b (CH3CClF2) to VDF (CH2=CF2) at 350 ◦C, which is signiﬁcantly lower than the industrial manufacture temperature (600–700 ◦C) by the thermal decomposition of HCFC-142b. However, for the BaF2 catalyst, the selectivity of VDF decreases from 94% to 84% along with the deactivation of the BaF2 catalyst monotonically. In the presence of small amounts of Cl in BaF2, stabilized selectivity is achieved. Over BaCl0.05F0.95, BaCl0.1F0.9 and BaCl0.25F0.75, no decrease in VDF selectivity is observed. According to XRD results, the presence of small amounts Cl during solid-state preparation disturb the formation of BaF2 crystalline signiﬁcantly. Despite the formation of BaClF after reaction, the particle size of the BaClxFy catalysts are still far smaller than that of BaClF and the spent BaClF. Hence, the activity of the BaClxFy catalysts with a low Cl content is still much higher than that of the BaClF after reaction. We suggest that the particle size, or more precisely, the crystal size of the barium catalyst play a major role in the catalytic performance. In addition to the crystal growth, the presence of small amounts of Cl during catalyst preparation changes the chemical state of Ba, and therefore the adsorption and activation of the C-Cl bond for HCFC-142b are altered.

Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4344/10/4/377/s1, Figure S1: XRD patterns of spent BaF2 and barium chlorofluoride catalysts; Figure S2: XRD patterns BaF2 catalysts calcined at temperatures between 300 ◦C and 600 ◦C; Figure S3: XRD patterns BaF2 catalysts calcined at temperatures between 300 ◦C and 600 ◦C; Figure S4: Effect of calcination on the conversion of HCFC-142b and selectivity to VDF for BaF2 catalysts; Figure S5: High resolution XPS spectra of SEM images of BaF2 and barium chlorofluoride catalysts following reaction with time on stream of 24 h. Author Contributions: Conceptualization, W.H.; methodology, W.H. and W.Y.; validation, W.Y., Y.L. (Yongnan Liu), J.L. and H.Y.; formal analysis, W.Y. and B.L.; investigation, W.Y., Y.L. (Yongnan Liu), J.L. and H.Y.; resources, W.H., H.T., A.C. and Y.L. (Ying Li); data curation, W.Y.; writing—original draft preparation, W.Y.; writing—review and editing, W.H.; visualization, W.Y.; supervision, W.H., H.T., A.C. and Y.L. (Ying Li); project administration, W.H.; funding acquisition, W.H. and A.C. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by Zhejiang Provincial Natural Science Foundation of China under grant no. LY19B060009 and LY19B050004. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. Catalysts 2020, 10, 377 11 of 13

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