USOO5804.153A United States Patent (19) 11 Patent Number: 5,804,153 Fang et al. (45) Date of Patent: Sep. 8, 1998

54 CATALYTIC REMOVAL OF SULFUR 5,028,310 7/1991 Pratt et al...... 208/121 DOXDE FORM FLUE GAS 5,242,673 9/1993 Flytzani-Stephanopoulos et al. ... 423/ 570 75 Inventors: Ming Fang; Jian Xin Ma, both of 5,399,327 3/1995 Kim ...... 423/244.11 Clearwater Bay; Ngai Ting Lau, Tai FOREIGN PATENT DOCUMENTS Po, all of Hong Kong 4384326 3/1988 U.S.S.R...... 423/437 M 73) ASSignee: The Hong Kong University Of OTHER PUBLICATIONS Science & Technology, Hong Kong, Hong Kong Ma et al. “Activation of La O. For The Catalytic Reduction of SO. By Co” J. of Catalysis, vol. 163 No. 2 pp. 271-278, 21 Appl. No.: 674,715 Oct.Baglio 1996. “lanthanum Oxysulfide AS A Catayyst for The Oxi 22 Filed: Jul. 2, 1996 dation of CO And COS By SO” Ind. Eng. Chem. Prod. Res. O O Dev.; Mar. 1982; vol. 21 No. 1 pp. 38–41. Related U.S. Application Data Hibert et al. “Flue Gas Desulphurisation: Catalytic Removal ...” Applied Catalysis, 41 (1988, No Month) pp. 289-299. 63 Continuation-in-part of Ser. No. 357,028, Dec. 16, 1994, abandoned. Primary Examiner-Gary P. Straub 6 Assistant Examiner Timothy C. Vanoy 51 Int. Cl...... B01D 53/50; B01D 53/62 Attorney, Agent, or Firm-Burns, Doane, Swecker & 52 U.S. Cl...... 423/242.1; 423/244.01; Mathis, L.L.P. 423/244.09: 423/247; 423/437 M; 423/570 s 58 Field of Search ...... 423/570, 437 M, (57 ABSTRACT 423/247, 244.09, 244.01, 424.1 The present invention discloses a method for the catalytic 56) References Cited reduction of Sulfur dioxide, for example in flue gas, by carbon monoxide using lanthanum oxySulfide as the active U.S. PATENT DOCUMENTS catalyst. The catalyst is prepared from lanthanum oxide by hydration and Sulfidization, the latter Step being carried out 3,914,3893,931,390 10/19751/1976 PalillaHaacke ...... 423/244423/263 in the gas Stream itself. This method of preparation has more 3,931,393 1/1976 Palilla 423/570 general applicability and can also be used as a method for 3,961,016 6/1976 Gerstein et al. . ... 423/247 the preparation of lanthanum, yttrium, gadolinium and lute 3,978,200 8/1976 Bajars ...... 42.3/570 tium oxySulfides generally. 4,022,870 5/1977 Palilla et al...... 423/244 4,589,978 5/1986 Green et al...... 208/113 8 Claims, 4 Drawing Sheets

100 O.O5

8O O.04

CO 8 S. CO C) 60 O.O3 9 dg s ce f S 40 O.02 3 s S. s

20 O.O1

O O 350 400 450 500 550 6OO Reaction Temperature / deg. C U.S. Patent Sep. 8, 1998 Sheet 1 of 4 5,804,153

COS Concentration 1 %

O w CY) CN w O d O O O O O O O O O O O CO

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O O cy) O O O O O O O OO CO V CN wm SO2 Conversion 1 % U.S. Patent Sep. 8, 1998 Sheet 2 of 4 5,804,153

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O O O O O O O LO CO CO H s (5 (5

O O O O 3 8 CO w CN SO2 ConCentration 1 % U.S. Patent Sep. 8, 1998 Sheet 3 of 4 5,804,153

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SO2 Concentration 1 % U.S. Patent Sep. 8, 1998 Sheet 4 of 4 5,804,153

(g02)(90) (Z09) O (Gl). Sl (2)(008) O OO (v02)(zz) (90) (v. k 3. (GOO) (802), (vocal H 3 (LOC) V (OOC) CD (COL) (Oll)

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s 3. 3 S. 3 S 5,804,153 1 2 CATALYTIC REMOVAL OF SULFUR Solid or liquid wastes, the products are carbon dioxide which DOXDE FORM FLUE GAS can be discharged into the atmosphere and almost pure Sulfur which may be used commercially, eg in the produc CROSS-REFERENCE TO RELATED tion of Sulfuric acid. Catalytic reduction with CO also has APPLICATION the advantage that CO may be already present in the gas Stream as a combustion product. This application is a Continuation-In-Part of U.S. Ser. No. A number of catalysts have been proposed for both the 08/357,028, filed Dec. 16, 1994 now abandoned. Claus process and also for catalytic reduction. U.S. Pat. Nos. 3,978,004, 4,062,932 and 4,374,819 describe the use of FIELD OF THE INVENTION lanthanum and other rare-earth containing catalysts in This invention relates to the removal of Sulfur dioxide Claus-type processes. U.S. Pat. No. 4,062.932 discloses the from waste gas Streams by catalytic reduction by CO using elimination of carbonyl sulfide by lanthanum oxysulfide and a novel catalyst comprising a rare earth oxysulfide Such as the use of a lanthanum oxide containing catalyst in a Claus lanthanum oxySulfide. The main products of the reduction reaction. The catalyst contains lanthanum oxide or other rare are carbon dioxide and elemental Sulfur. The invention also 15 earth oxides or a mixture of rare-earth and transition metal extends to a method for preparing lanthanum oxySulfide and oxides. The pre-treatment of the catalyst involves hydrogen other rare earth oxySulfides. Sulfide as the only or major component. The desulfurization process itself has three Stages: two Claus StepS and one BACKGROUND OF THE INVENTION oxidation Step at the end to minimize hydrogen Sulfide and Sulfur dioxide discharged into the atmosphere as a carbonyl Sulfide emission. by-product of fuel combustion and ore roasting processes is U.S. Pat. Nos. 3,931,390, 3,931,393, 3,978,200 and one of the major components of acid rain and other forms of 4,022,870 describe the use of mixed metal oxide catalysts in atmospheric pollution. The need for sulfur dioxide removal the reduction of Sulfur dioxide to elemental Sulfur. The is well established but the high cost of existing processes catalysts contain a rare-earth oxide Such as lanthanum, (including the disposal of by-products) has prevented the 25 yttrium, gadolinium or cerium oxide, and one other metal wide application of Sulfur dioxide removal from coal-fired oxide Such as cobalt, Zirconium or titanium oxide. power plants, Smelters etc. U.S. Pat. No. 5,242,673 describes a Sulfur dioxide reduc There are many existing processes: wet and dry Scrubbing tion proceSS using a cerium oxide catalyst. This proceSS is a are among the more popular methods. These Scrubbing Single-stage catalytic reduction of Sulfur dioxide in the feed methods use a large amount of liquid/solid Sorbents to gas to elemental Sulfur. However the catalyst has very low absorb Sulfur dioxide, turning the harmful gaseous pollutant productivity (space velocity of 2000 hr' as shown in their into liquid or solid forms which then require further treat examples) and from the inventor's published literature it is ment and/or disposal. The capital and running costs of Such apparent that it is not water resistant. Systems are generally high, the operation is complicated and The use of lanthanum oxysulfide in combination with a 35 transition metal Sulfide (eg CoS) as a catalyst for the the processes involved are not especially “clean”. reduction of Sulfur dioxide by carbon monoxide has been Today, many countries have industries that emit large reported by Baglio (Ind. Eng. Chem. Prod. Res. Dev 1982, quantities of Sulfur dioxide in flue gas for energy needs, 21, pp 38-41) where the process is a two-step reaction with while at the same time mining elemental Sulfur for the the transition metal Sulfide being an essential component. production of Sulfuric acid, which is the Second largest 40 However, Baglio Specifically reported that lanthanum quantity of chemical produced in the World. It would there Oxysulfide alone had no catalytic effect and minimal reduc fore be beneficial to find a commercially viable process of tion of Sulfur dioxide was observed. obtaining elemental Sulfur from Sulfur dioxide in flue gas. SUMMARY OF THE INVENTION PRIOR ART 45 The present inventors have discovered that contrary to the One known proceSS is the Claus process. The main teachings of the prior art rare earth oxySulfides and reaction of the Claus process is: Oxysulfide/OXydisulfide mixtures alone may be a highly efficient catalyst. According to the present invention there is provided a method for the catalytic reduction of Sulfur 50 dioxide to elemental Sulfur employing the reduction The Claus proceSS has been used for many years in reaction, refineries or where hydrogen Sulfide is readily available. Unfortunately the process is handicapped by the fact that it requires the correct Stochiometric ratio between the reactants 55 and cannot tolerate the presence of oxygen. Furthermore it wherein Said reaction is carried out in the presence of a is a multistage process. When it comes to flue gas hydrogen catalyst comprising a rare earth oxySulfide or oxySulfide/ Sulfide is not normally present in Substantial quantities and OXydisulfide as the only active component at a temperature it is necessary to generate a Supply of hydrogen Sulfide. of between 350° C. and 750° C. Sulfur dioxide can also be removed by catalytic reduction 60 It has been discovered by the present applicants that a methods, eg by carbon monoxide: particularly preferred rare earth element for this catalytic reaction is lanthanum and lanthanum oxySulfide is a highly effective catalyst for the reduction of sulfur dioxide by carbon monoxide. There is no report in the literature that With a suitable catalyst complete reduction can be 65 Suggests that lanthanum oxysulfide is an effective catalyst achieved with minimal generation of Side products. Unlike for this reaction. The catalyst may be either Supported or the Scrubbing methods this method does not produce any unsupported, and may of course comprise either Substan 5,804,153 3 4 tially pure lanthanum oxySulfide or a mixture including inert gas purge, eg using nitrogen at between 600 to 750 lanthanum oxySulfide. C. for at least two hours. The purification can also be done In this reaction the lanthanum oxySulfide catalyst may be at a lower temperature in vacuum. prepared by activation of lanthanum oxide in a reaction It has also been found that the oxysulfides and oxysulfide/ Stream containing Sulfur dioxide and carbon monoxide at not OXydisulfide mixtures of other rare earth elements, Such as less than 400 C. The reaction temperature is preferably yttrium, gadolinium, lutetium, neodymium, dySprosium and between 400° C. and 700° C. and more preferably from 500 europium, prepared in this way may also serve as catalysts C. to 600 C. With a space velocity for the gas stream of for the reduction by CO of SO. between 2000 to 30,000 hr' a conversion from sulfur dioxide to elemental sulfur of 80% to 100% may be BRIEF DESCRIPTION OF THE DRAWINGS achieved. The lanthanum oxide is preferably hydrated prior to being placed in the reaction Stream. Any convenient Several examples illustrative of preferred embodiments of hydration method may be employed but it is particularly the present invention will now be described with reference Simple to expose the lanthanum oxide to ambient atmo to the accompanying drawings, in which: sphere for a required time (depending on atmospheric 15 FIG. 1 shows the SO conversion and COS formation as conditions), or to expose the oxide to an atmosphere Satu a function of the reaction temperature, rated with water vapour. Other possibilities for the hydration FIG.2 shows the SO conversion as a function of oxygen Step include heating and refluxing with an excess of water. concentration, The method of preparing the lanthanum oxySulfide from FIG. 3 shows the effect of the presence of water, and lanthanum oxide as a catalyst for the reduction to elemental FIG. 4 shows the results of X-ray diffraction analysis in sulfur of sulfur dioxide by carbon monoxide has the advan Example 11. tage that the Sulfidization Step may be performed in the gas Stream itself. DETAILED DESCRIPTION OF EXAMPLES The method of the present invention has the advantage that the conversion from Sulfur dioxide to elemental Sulfur 25 Desulfurization Examples involves only one Stage making the process Simple to design and operate. In addition there is low COS formation (a Example 1 known problem with prior techniques), and a high conver An externally heated fixed-bed reactor fabricated from a Sion rate. A further advantage is that the catalyst can be 2 cm diameter by 50 cm long quartz tube was used in the prepared from low cost Simple starting materials. experiments described in these examples. The temperature The method of activating the catalyst by preparing the of the catalyst bed was controlled to within 1 C. and the oxySulfide from the oxide has more general applicability and feed gas was fed from the top of the reactor. the same method in essence may be used to prepare the A gas mixture containing 0.5% mol SO, 1.0% CO and oxysulfides of other rare earth elements (RE) such as UHP N entered the reactor at a constant flow rate of 180 yttrium, gadolinium, and lutetium in addition to lanthanum 35 ml/min measured at atmospheric pressure. in a particularly simple and cheap manner. Such oxysulfides have other industrial applications, but currently are very CO and unconverted SO concentrations in the reactor expensive. exhaust were measured using non-dispersive infra-red ana lyZers. A gas chromatograph with two columns and TCD Accordingly the present invention also extends to a detectors was used in parallel to determine the unconverted method for preparing the oxySulfide of the rare earth ele 40 ments eg lanthanum, yttrium, gadolinium or lutetium from CO, any side-products formed and unconverted SO2 (as a the rare earth oxide, comprising the Steps of: double check). Elemental sulfur was removed from the (1) hydrating the rare earth oxide to form the hydroxide, product gas Stream by passing the gas through an ice-bath and trap and a filter with an average pore size of 2 um. (2) Sulfidizing the resulting hydroxide by reacting with 45 Half a gram of LaOS catalyst prepared from La O by carbon monoxide and Sulfur dioxide. hydration by exposure to atmosphere and Sulfidization at These steps may be followed by a purification step if 600° C. method (as will be described in more detail below necessary. It is possible to omit the hydration Step, but in this in Example 15) was used. This corresponded to a gas space case the reaction time is much longer. Again the hydration velocity of 21,600 ml/hr.g. The activity and selectivity of the Step may comprise exposure to ambient atmosphere for a 50 catalyst measured at different temperatures are shown in Sufficient period of time, exposure to atmosphere Saturated FIG.1. The only detectable side-product was COS. The SO with water vapour, refluxing with water, or any conventional conversion increased with the reaction temperature while the hydration technique. formation of COS went through a maximum at around 400 C. At 600° C., the SO conversion was 96% and the The Sulfidization can be carried out at a temperature of selectivity was 98.4%. from 400° C. to 1200° C., and preferably from 550° C. to 55 750° C. Preferably the ratio of carbon monoxide to Sulfur The catalyst was characterized after the experiment by dioxide is 2:1 on a molar basis. XRD (X-ray diffraction) and no change in structure was Sulfidization of decomposition products of RE(OH), detected. formed by exposing REO to atmosphere, which include Contrary to the literature where it was reported that RE(OH), REOOH, REO and not excluding RE(OH) 60 LaOS was not an effective catalyst for the reduction of COnH2O, REOCO and mixtures of these compounds, is SO using CO, our experiment showed that active La OS also possible using this process. can be made from La2O and is a very effective catalyst for In the sulfidization step elemental Sulfur, formed from the the reaction. reduction of SO by CO, and other substances may be Example 2 adsorbed on the surface of the oxysulfide. To raise the purity 65 of the product therefore a purification Step may be One hundred grams of 99.99% pure LaO powder was employed. Preferably this step comprises a high temperature hydrated by exposure to air for at least 6 months to form a 5,804,153 S 6 sample of La(OH), with a specific Surface area of 6.46 m/g, tion of oxygen in the reaction gas mixture was varied to as is described below in Example 16. Study the effect of oxygen on the catalyst. A Series of Simultaneous Sulfiding and reduction experi The effect of oxygen on the SO conversion is shown in ments were carried out with the conditions described in FIG. 2. It can be seen that the conversion decreased slowly Example 1. The ratio of CO/SO in the feed stream was 5 when more oxygen was present and the influence of oxygen varied and the gas Space Velocity was changed by changing could be inhibited by increasing the reaction temperature. At catalyst weight and feed flow rate. The results are presented an oxygen concentration of 2.0% and 650 C., the conver in Table 1. The results show that by increasing the CO/SO sion was 85.3% and the selectivity was 91.7%. It was also ratio, almost complete reduction of SO can be obtained at found that after about 10 hours of exposure to the oxygen about 450° C. containing gas stream at temperatures above 600 C., the

TABLE 1. Weight Space of catalyst velocity CO/SO, SO, Conversion (% Selectivity (% (g) (ml/hrg) ratio 450 C. 500 C. 550 C. 600 C. 450 C. 500 C. 550 C. 600 C. 0.5 21,600 2.OO 90.1 95.1 95.8 95.1 98.2 98.4 98.3 98.6 1.O 6,000 2.26 1OO 1OO 1OO 1OO

Example 3 catalyst did not change Structure and remained as LaOS. This example shows that the catalyst of the present invention A Sample of catalyst with a specific Surface area of 3.37 can be used in an oxygen containing environment. m/g, was prepared by hydration by exposure to atmosphere 25 and sulfidization as described in Example 17 below. The Example 7 catalyst was used for the reduction of SO with CO; the SO The procedure in Example 1 was repeated to test the conversion and selectivity at 600 C. with a space velocity resistance of this invention to moisture by injecting water of 6,000 ml/hrig were 98.1% and 95.6%, respectively, and during the reaction. Half a gram of A-La-O was used and 94.4% and 97.5% at a space velocity of 21,600 ml/hr.g. the results are shown in FIG. 3. Example 4 It can be seen that the A-La-O was quickly activated after the injection of the first 0.05 ml of water into the reactor. The A Sample of 44.5 grams of La O was hydrated by the Subsequent introduction of water after steady-state was exposure to atmosphere method as described in Example 2, established caused a decrease in SO conversion, however, was calcined at 900 C. for 12 hours and cooled to room 35 temperature. The calcination product was 41.0 grams of each time it did not take long to regain the Steady-state value. powder and XRD analysis showed that it was A-La-O. The This example indicates that the hydration and Sulfidization specific Surface area of the A-La-Os was 6.35 m/g (see StepS can be carried out simultaneously and the catalyst of Example 18 below). the present invention is water resistant. The reduction procedure of Example 1 was repeated using 40 Example 8 (For Comparison) only 0.5 gram of the A-La-O as catalyst. The activity and A mixture containing 3.26 g of 99.99% pure LaO and selectivity measured after 2 hours reaction were 70% and 6.00 g of 97% pure Co(NO),.6HO was ground in a ball 99%, respectively. XRD analysis revealed that a significant mill and transferred to a ceramic crucible. The Sample was amount of La O was found even after a reaction time of 7 calcined in a furnace at 750° C. for 8 hours. After cooling to hours. 45 room temperature, the Sample was ground to pass a 200 mesh sieve and calcined again at 800° C. for 9 hours. After Example 5 cooling, the Sample was ground once more and re-calcined The procedure of Example 4 was repeated with the at 900 C. for 10 hours. XRD analysis showed the sample hydration Step carried out in a quartz tube and followed by has only a single perovskite, LaCoO, phase. the in Situ calcination of the catalyst precursor. 50 A Sample of the powdery material weighing 0.5 g was After two hours of experiment at 600 C., the SO placed in the quartz reactor and was Sulfidized in the same conversion and selectivity were 64% and 98% respectively. manner as described in Example 1. By extending the reaction time to 28 hours, the conversion After a reaction time of 8 hours at 600 C., the SO increased to 89.5% and the selectivity decreased to 96.2%. conversion and selectivity were 95.7% and 97.9%, respec XRD analysis showed that almost all of the sample was 55 tively. XRD characterization found that the perovskite was converted to La-OS at the end of the experiment. decomposed by the reaction and the lanthanum part of the Examples 4 and 5 clearly indicate that La-O can be crystal was sulfidized to form LaOS while the cobalt was activated by Sulfiding in the reduction gas mixture Stream to Sulfidized to form CoS and CoSooz. form the oxysulfide catalyst, however, the time required is It is clear from this investigation that the oxysulfide is the much longer than when a hydration Step was used. This may 60 active ingredient in the mixture; the perovskite, LaCoO, be one of the reasons why the other investigators harvested can be a catalyst precursor but it is not any more Superior to the opinion that La O is inactive as a catalyst for the SO the simple La(OH) preferred by the preparation method reduction. disclosed.

Example 6 65 Example 9 The procedure of Example 3 was repeated except 0.5 The procedure of Example 1 was repeated with 0.5 grams gram of the catalyst, La OS, was used and the concentra of yttrium oxide (YO) at 600° C. The conversion of Sulfur 5,804,153 7 8 dixoide was 88% at steady state. XRD showed that the introduced. The Sample was Sulfidized according to a tem Sample was converted to a mixture of yttrium oxide (YO) perature programmed sequence: 600 C. for 2 hours, 650 C. and yttrium oxysulfide (YOS). for 4 hours, 700° C. for 6 hours and 750° C. for 8 hours. XRD analysis showed that well crystallized single phase Example 11 LaOS was formed (see FIG. 4). The LaOS prepared had The procedure of Example 1 was repeated with 0.5 grams specific surface area of 3.37 m/g. of neodymium oxide as received, which was shown to contain neodymium oxide (Nd2O) and neodymium hydrox Example 18 ide (Nd(OH)) at 600° C. The conversion of sulfur dioxide A 44.5 gram Sample of La-O was hydrated by the method was 93% at steady state. XRD showed that the sample was described in Example 16. It was calcined at 900 C. for 12 converted to neodymium oxysulfide (NdOS). hours and cooled to room temperature, resulting in 41.0 grams of product in powder form. XRD analysis showed that Example 12 the heat treated product was A-La-O with a specific Surface The procedure of Example 1 was repeated with 0.5 grams 15 area of 6.35 m/g. of europium oxide (EuO) at 600° C. The conversion of The Sulfiding procedure in Example 15 was repeated sulfur dioxide was 85% at steady state. XRD showed that the except 0.5 gram of the A-La-O was used. XRD analysis Sample was converted to a mixture of europium oxide revealed that a significant amount of LaO remained even (Eu2O) and europium oxysulfide (Eu2O2S). after a reaction time of more than 7 hours. Example 13 Example 19 The procedure of Example 1 was repeated with 0.5 grams The procedure in Example 18 was repeated and water of gadolinium oxide (Gd2O) at 600° C. The conversion of Vapor was injected into the reactor during the Sulfidization sulfur dioxide was 93% at steady state. XRD showed that the reaction. XRD analysis showed that the A-La-O was con Sample was converted to gadolimium oxide (Gd2O) and 25 verted to oxysulfide. This demonstrates that hydration and gadolinium oxysulfide (Gd2O2S). Sulfidization can be carried out in one-step. Example 14 Example 20 The procedure of Example 1 was repeated with 0.5 grams A 5.0 gram sample of La(OH) formed by exposure in of dysprosium oxide (DyO) at 600° C. The conversion of atmospheric moisture was calcined at 400° C. for 12 hours. sulfur dioxide was 79% at steady state. XRD showed that the XRD analysis identified that LaCOH was formed as a Sample was converted to a mixture of dysprosium oxide decomposition product. (DyO) and dysprosium oxysulfide (DyOS). Half a gram of the LaCOH powder was placed in a quartz 35 reactor and sulfidized by the method as described in Examples of the Preparation of Oxysulfide Example 15. It was found that in addition to LaOS a Example 15 Significant amount of LaOS was formed. Five grams of 99.99% pure La O powder was calcined Example 21 in a furnace at 900 C. for 12 hours and cooled in air to room 40 Half a gram of the La(OH) formed by exposure in temperature. XRD (X-ray diffraction) analysis showed that atmospheric moisture was placed in a quartz tube. The only A-La-O phase existed in the Sample. The Sample was sample was decomposed at 400° C. under vacuum (10ft) hydrated by placing in a closed container under atmosphere for 2 hours. The sulfidization procedure of Example 15 was Saturated with water at room temperature for one week. used. XRD analysis showed that the product was a mixture XRD analysis revealed that this treatment led to a complete 45 of La OS and La-OS. conversion of La-O to La(OH). We claim: Half a gram of the pretreated Sample was used as Starting 1. A method for the catalytic reduction of sulfur dioxide material and was Sulfided in a quartz reactor under a gas to elemental Sulfur employing the reduction reaction stream containing 0.5% v SO, 1.0% v CO and 98.5% v N. at 600 C. for 2 hours. The Sulfided material contained 50 neither La-O nor LaCOH), when analyzed by X-ray dif fraction; the only distinct phase was LaOS. wherein Said reaction is carried out in the presence of a Example 16 catalyst consisting essentially of a rare earth oxySulfide or 55 Oxysulfide/OXydisulfide mixture as the only active compo One hundred grams of 99.99% pure LaO powder was nent at a reaction temperature of between 350° C. and 750 exposed to air for at least 6 months. The moisture in the C. wherein said rare earth oxysulfide or oxysulfide/ atmosphere was sufficient to hydrate the material. The thus OXydisulfide is prepared by Sulfidization of a hydrated rare obtained sample had a specific Surface area of 6.46 m/g and earth oxide at a temperature between about 400° C. and was completely converted to La(OH) when examined using 60 about 900 C. XRD. The Sulfiding procedure as outlined in Example 15 2. A method as claimed in claim 1 wherein Said rare earth was used to completely convert the product to LaOS. is Selected from the group consisting of lanthanum, yttrium, gadolinium, lutetium, neodymium, dysprosium and Example 17 europium. LaOS was prepared as follows: 5.0 grams of the air 65 3. A method as claimed in claim 1 wherein said hydrated exposed La-O as described in Example 10 was placed in a rare earth oxide is obtained by exposing rare earth oxide to quartz reactor and a gas mixture containing SO and CO was ambient atmosphere. 5,804,153 10 4. A method as claimed in claim 1 wherein said hydrated 7. A method of claim 1, wherein said catalyst is lanthanum rare earth oxide is obtained by exposing rare earth oxide to Oxysulfide or a lanthanum oxySulfide/oxydisulfide mixture. water vapour. 5. A method as claimed in claim 1 wherein the catalyst is 8. The method of claim 7, wherein said catalyst is Supported. 5 lanthanum oxySulfide. 6. A method as claimed in claim 1 wherein the catalyst is unsupported.