Influence of the Obtaining Method on the Properties of Amorphous
Total Page：16
File Type：pdf, Size：1020Kb
coatings Article Influence of the Obtaining Method on the Properties of Amorphous Aluminum Compounds Aliya N. Mukhamed’yarova *, Oksana V. Nesterova, Kirill S. Boretsky, Juliya D. Skibina, Avgustina V. Boretskaya, Svetlana R. Egorova and Alexander A. Lamberov Alexander Butlerov Institute of Chemistry, Kazan Federal University, Kazan 420008, Russia; [email protected] (O.V.N.); [email protected] (K.S.B.); [email protected] (J.D.S.); [email protected] (A.V.B.); [email protected] (S.R.E.); [email protected] (A.A.L.) * Correspondence: [email protected]; Tel.: +7-960-051-3178 Received: 1 December 2018; Accepted: 10 January 2019; Published: 14 January 2019 Abstract: Amorphous aluminum compounds are formed during the synthesis of the γ-Al2O3 catalyst precursor. Amorphous compounds influence on the alumina catalyst variously due to different physicochemical properties, which depend on the method of their preparation. In this research, the comparative analysis of physicochemical properties of amorphous aluminum compounds that were obtained by the precipitation method, the thermal decomposition of aluminum nitrate, and alcoxide hydrolysis product were studied. It is the first time that a new method for calculating of quantitative phase composition of amorphous aluminum compounds using the X-ray powder diffraction, thermogravimetric and differential scanning calorimetry analysis, mass-spectrometry, and CHN-analysis was described. Properties of obtaining samples were studied using scanning electron microscopy, low-temperature nitrogen adsorption, and temperature programmed desorption of ammonium analyses. The methods of precipitation and thermal decomposition of aluminum nitrate allows for obtaining non-porous samples consisting of a mixture of amorphous phases (hydroxide and basic salt) that contain the metals impurities and have low acidity of the oxides obtained from them. The highly porous amorphous alumina formed by the thermal decomposition of the alcoxide hydrolysis product with the least amount of impurities and a high acidity of the surface was observed. Keywords: amorphous aluminum compound; alumina catalyst; alumina; pseudoboehmite; precipitation; thermal decomposition 1. Introduction Gamma-alumina (γ-Al2O3) is widely used in the petrochemical industry as a catalyst, catalyst carrier, and adsorbent. γ-Al2O3 is formed during the thermal decomposition of the boehmite [1], obtained from the sol-gel method from bayerite [2], bauxite [3], salts and salt-like aluminum compound [4–6], amorphous aluminum oxide, and hydroxide [5,7]. Depending on the nature and characteristics of the precursor, it is possible to regulate the physicochemical properties of γ-alumina. One of the most important characteristics of the catalyst precursor is the properties of its surface, such as morphology, porous system, and acidity. On an industrial scale, γ-Al2O3 is predominantly produced by the thermal decomposition of pseudoboehmite (PB). There are many methods for the synthesis of PB, for example, a hydrothermal treatment of gibbsite or alumina, a precipitation from solution salts under hydrothermal conditions [8,9], and others. However, the most common methods of PB obtaining are the hydrolysis of aluminum alkoholates [10] and the precipitation of aluminum hydroxide from Al-containing acidic solutions by a base [11]. These methods allow for controlling the phase composition and physicochemical properties of the obtained aluminum hydroxides. In both cases, the formation of Coatings 2019, 9, 41; doi:10.3390/coatings9010041 www.mdpi.com/journal/coatings CoatingsCoatings2019 2018, ,9 7,, 41 x FOR PEER REVIEW 22 ofof 14 13 Coatings 2018, 7, x FOR PEER REVIEW 2 of 13 properties of the obtained aluminum hydroxides. In both cases, the formation of amorphous amorphouspropertiescompounds of compounds is theobserved obtained is in observed addition aluminum into additionthe hydroxides target to pr theoduct. targetIn dueboth product to cases, the forming due the to formation the of formingincomplete of of amorphous incomplete hydrolysis hydrolysiscompoundsproducts in products isthe observed first incase the in and addition first the case organic to and the the targetresidues organic pr oductinresidues the duesecond to in the thecase, forming second in accordance of case, incomplete inaccordance with Schemehydrolysis with 1. Schemeproducts1. in the first case and the organic residues in the second case, in accordance with Scheme 1. SchemeScheme 1.1.Forming Forming ofof X-rayX-ray amorphousamorphous aluminumaluminum compoundscompounds byby the the precipitation precipitation and and hydrolysis. hydrolysis. Scheme 1. Forming of X-ray amorphous aluminum compounds by the precipitation and hydrolysis. Currently,Currently, thethe amorphousamorphous aluminumaluminum compoundscompounds havehave beenbeen studiedstudied poorlypoorly andand theythey areare describeddescribedCurrently, inin aa small smallthe amountamorphousamount ofof research researchaluminum works. works. compounds However,However, have thesethese been compoundscompounds studied affect affectpoorly thethe and propertiesproperties they are ofof γdescribedγ-Al-Al22OO33 catalysts. in a small amount of research works. However, these compounds affect the properties of γ-Al2OnOOn3 catalysts. thethe oneone hand,hand, the amorphous component component presence presence as as a a part part of of alumina alumina catalyst catalyst precursor precursor in invarious variousOn thepetrochemical petrochemical one hand, the processes processes amorphous is isunfavorable. unfavorable.component Th presence Thee amorphous amorphous as a part compound compoundof alumina is a iscatalyst gel a gelthat that precursor reduced reduced the in thevariousfilterability filterability petrochemical of the of theprecipitation precipitation processes product is unfavorable. product and and complica Th complicatede amorphousted the thewashing compound washing of PB of isfrom PB a gel from impurity that impurity reduced ions ions(Na, the (Na,filterabilityFe, etc.) Fe, etc.)that of are thatthe catalytic precipitation are catalytic poisons. poisons.product In addition, and In addition, complica the amorphous theted the amorphous washing component componentof PB has from a lowimpurity has specific a low ions specific surface (Na, surfaceFe,area etc.) [12]. areathat Therefore, [are12]. catalytic Therefore, the amountpoisons. the amountof In the addition, amorphous of the the amorphous amorphous component component component in the PB in is has thereduced a PB low is specificat reduced the synthesis surface at the synthesisareaprocess. [12]. process.Therefore, the amount of the amorphous component in the PB is reduced at the synthesis process.OnOn the the other other hand, hand, the amorphousthe amorphous component component has a positivehas a effectpositive on theeffect catalyst. on the An catalyst. amorphous An baseamorphousOn aluminum the baseother salts aluminum hand, provide the salts theamorphous provide plastic propertiesthecomponent plastic ofproperties ha thes a catalyst positive of the precursor catalysteffect on duringprecursor the catalyst. a molding.during An a Theamorphousmolding. salts decomposeThe base salts aluminum decompose with the salts with formation provide the formation athe new plastic binding a new properties binding phase of afterphase the thecatalyst after calcination the precursor calcination [13]. during In[13]. our Ina previousmolding.our previous works The saltsworks [14], decompose we [14], have we already havewith thealready shown formation thatshown it isa possiblethnewat itbinding is topossible improve phase to theafter improve properties the calcination the ofproperties catalyst [13]. for Inof skeletalourcatalyst previous isomerization for skeletalworks [14],isomerization of n-butenes we have to alreadyof isobutylene n-butene showns byto th transformingatisobutylene it is possible theby amorphoustransformingto improve componentthe the properties amorphous using of hydrothermalcatalystcomponent for usingskeletal treatment. hydrothermal isomerization treatment. of n-butene s to isobutylene by transforming the amorphous componentThereThere areusingare severalseveral hydrothermal waysways toto obtaintreatment.obtain the the amorphous amorphous aluminum aluminumcompounds: compounds: aa calcinationcalcination ofof thethe aluminumaluminumThere saltsaresalts several [[7],7], the ways hydrolysis hydrolysis to obtain of of the the aluminum aluminumamorphou alcoholatess alcoholatesaluminum [15], [compounds:15 ],and and the the precipitation a precipitation calcination from of from theAl- Al-containingaluminumcontaining salts solutions solutions [7], the by byhydrolysisthe the base base [7,16]. of [7, 16the As]. aluminum Asa resu a result,lt, various alcoholates various non-crystalline non-crystalline [15], and thealuminumaluminum precipitation compounds compounds from Al- are arecontainingformed formed differing differingsolutions in in aby phase a the phase base composition composition [7,16]. As anda and resu the thelt, physicochemical various physicochemical non-crystalline properties aluminum of surface.surface. compounds High-purityHigh-purity are amorphousformedamorphous differing aluminumaluminum in a phase hydroxidehydroxide composition containingcontaining and the thethe physicochemical organicorganic residuesresidues properties isis obtainedobtained of bysurface.by thethe hydrolysishydrolysis High-purity ofof organoaluminumamorphousorganoaluminum aluminum compound.compound. hydroxide The The