WO1999043195A2

WO1999043195A2 - A catalyst based on titanium and method for its preparation

Info

Publication number: WO1999043195A2
Application number: PCT/IL1998/000091
Authority: WO
Inventors: Ya'acov Mirsky
Original assignee: Rotem Amfert Negev Ltd
Current assignee: Rotem Amfert Negev Ltd
Priority date: 1998-02-24
Filing date: 1998-02-24
Publication date: 1999-09-02
Anticipated expiration: 2000-08-24
Also published as: AU6228498A

Description

A CATALYST BASED ON TITANIUM AND METHOD FOR ITS

PREPARATION

The present invention relates to a novel catalyst. More particularly, the invention relates to a novel catalyst, based on titanium dioxide to be most useful for the sulfur recovery in various processes.

BACKGROUND OF THE INVENTION.

The novel catalyst according to the present invention can be used in various processes and particularly in the sulfur recovery and various reactions which involve sulfur constituents, such as hydrogen sulfide reaction with sulfur dioxide (known as Claus reaction), carbonyl sulfide hydrolysis, carbonyl disulfide hydrolysis and direct oxidation of hydrogen sulfide with air and tail gases treatment (for example "Sulfreen" process). The catalyst can be used also in other catalytic processes in which titanium dioxide imparts catalytic activity, such as: carbon monoxide oxidation, nitrogen oxide reduction with ammonia, total oxidation of organic compounds, etc. There are various patents which deal with the titania-based catalyst preparation. According to the U.S. Patent No. 4,388,288, a shaped titanium dioxide catalyst or a carrier, is described. A suspension of titanium dioxide, obtained after hydrolysis and filtration in the conventional process of ilmenite treatment with sulfuric acid, was dried at a temperature below 200°C . As known, this material appears as a powder which is a partially crystalline anatase, being mainly used as a white titanium pigment. The powder has a weight loss on ignition in the range of between 1% to 50%, generally being mixed with water in the range of between 1% to 15% by weight and from 0% to 15% by weight of a shaping additive. The resulted mixture is shaped and the obtained article is dried and calcined. A poor crystallized anatase can also be obtained by the hydrolysis of titanium compounds having the general formula TiCl₄-n(OR)_n wherein "n" is in the range of between 0 to 4 and R is an alkyl radical. Another way to obtain this anatase is by precipitation of a titanium salt with a base constituent such as ammonia.

According to the U.S. Patent No. 4,511 ,668, a catalyst is suggested for the hydrolysis of carbonyl sulfide. The catalyst was prepared in the form of porous blocks or granules, wherein the main constituent of the blocks is titanium dioxide mixed with reinforcing materials, selected from silica, aluminium oxide, clay or aluminosilicate. The amount of reinforcing material used is limited up to 30% by weight; no data are mentioned on the properties of the specific reinforcing materials and their combination with the titanium dioxide. The materials mentioned in the various Examples are spherical carrier comprising Titanium dioxide up to 93%, SiO₂ up to 34% and AI₂O₃ 3% (all by weight). The catalysts contain also metal oxides in the range of between 0.5% to 10% by weight, the metal being selected from Li, Na, K, Cs, Mg, Ca, Ba, Zn, Cd. Sn, Pb or the like.

According to the U.S. Patent No. 4,422,958 a shaped titanium dioxide catalyst is obtained by the same procedure as described in the U.S. Patent No. 4,388,288 but comprises besides titanium dioxide, a sulfate of an alkaline earth metal selected from the group consisting of calcium, barium, strontium and magnesium. Three methods of the addition of the alkaline earth metal sulfate may be used. According to one method, a shaped titanium dioxide body is successively impregnated with a compound which provides the sulfate anion and then with a compound which provides the alkaline earth metal cation. According to the second and the third methods, the above mentioned compounds are transformed into the respective constituents to be incorporated in the mixture of titanium dioxide, water and shaping additive, before the step of this mixture shaping. According to the U.S. Patent No. 4,479,928, a catalyst for production of sulfur from a gas containing hydrogen sulfide is described. The catalyst comprises a porous matrix associated with metal compounds, such as Fe, Cu, Zn, Cd, Mo, W, and optionally a noble metal. The porous matrix comprising silica, titanium dioxide, zirconium dioxide, zeolites or alumina, are obtained by precipitating a hydrogel of silica, titanium or zirconium oxyhydrate from the respective solutions, followed by their transformation in pellets or beads being further dried and calcined. A mixed matrix can be produced by mixing the selected oxides prepared separately by a respective co-precipitation. According to the PCT patent application WO87/02654 a process is described for the removal of sulfur-containing compounds from residual gas, using three groups of catalyst:

(1) a metal associated with silica or alumina carriers;

(2) titanium dioxide containing calcium sulfate, and

(3) metal compounds associated with silica or titanium dioxide carrier containing some alumina.

According to the European patent No. 389,041, titanium extrudates are prepared from rutile and anatase in the form of shapable dough containing a mixture of titania with alkanolamine or ammonia, which are dried and calcined. It is mentioned the option to incorporate into the dough also other oxides, such as silica or zirconia and crystalline silicates. The resulted titania extrudates are suggested to be used as carriers for catalysis in hydrogenation processes and hydrocarbon conversion processes. There are cases where it is desirable to use an extrudable dough formed by a mixture of titanium dioxide, monoethanolamine, water, a powdery silica, zirconium dioxide and zeolite.

According to the French Patent Application No. 8606261, it is suggested a catalyst for the Claus process based on zirconium dioxide, optionally combined with titanium dioxide or cerium dioxide. The above brief review clearly illustrates the great interest for an improved catalyst useful for production of sulfur from a gas containing sulfur constituents or its removal from the surrounding. BRIEF DESCRIPTION OF THE INVENTION

The invention relates to a novel catalyst composition based on a modified titanium dioxide as a catalytic active component, as described in our copending PCT patent application No. and comprises at least 3% by weight of said catalytic active component, an inert filler selected from siliceous materials, most preferably being diatomaceous earth. There are cases where a binder component, such a sol of silicic acid may be used to prepare a catalyst generally in the form of extrudates. These extrudates possess a hardness above that of a commercial Claus catalyst, optimum macropore and mesopore structure and a high thermal stability as measured by a specific surface area up to 130 m²/g for a catalyst composition , comprising 45% by weight of the above mentioned modified titanium dioxide calcined at 800°C for three hours and a high hydrothermal stability. The above novel catalyst was found to be most useful in the sulfur recovery processes, such as Claus reaction, carbonyl sulfide hydrolysis, carbon disulfide hydrolysis and "Sulfreen" process.

DETAILED DESCRIPTION OF THE INVENTION

According to an embodiment of the invention the catalyst composition contains between 3% to 100% (by weight) of an active component which is selected from modified titanium dioxides or titanium hydroxides (calculated as titanium dioxides) as described in our copending PCT patent application No or their mixture in any proportion. Also useful, is a mixture of aforesaid modified titanium dioxide with another titanium dioxide or titanium hydroxide produced by any method, present in the mixture in a quantity of between 0% to 80% by weight, the balance being a filler with or without a binder material. In the catalyst composition, optionally a binder constituent in an amount of between 0% to 20% by weight may be introduced.

Different colloidal sols or hydrogels of silicic acid can be used as a binder component, but this catalyst can be also prepared without any binder. Different silica materials can be used as a filler, a preferable one being a natural silica-diatomaceous earth such as, or preliminary purified by an acid treatment from impurities of sodium, potassium, calcium, magnesium, and aluminium. Common mineral acids, such as hydrochloric acid or sulfuric acid can be used for this purpose. In order to reach a significant purification, the acid treatment has to be carried out at an elevated temperature in the range of between 60°C-100°C for 0.5-3 hours and the diatomaceous earth has to be washed from the acid solution. This diatomaceous earth can be used in the form of a water suspension, wet cake, or dried material. Another silica material which can be used as a filler, is selected from precipitated silica or silica hydrogels. If these materials contain even a small amount of sodium or potassium (about 1% by weight) it is advisable to eliminate these impurities by an acid treatment or with any other known method. Thus, the main components of this catalyst are: titanium dioxide and silica filler; titanium dioxide imparts a catalytic activity, while the silica filler imparts the necessary pore structure which causes a high rate of reagents diffusion inside the granules, the shaped catalyst and also to the reaction products outside the catalyst structure. For this purpose, diatomaceous earth porous structure consisting of macropores with diameter about 1 micrometer, is the best filler. Precipitated silica with low surface area and without a developed micropore structure and silica hydrogel with similar properties can also be used as fillers. The catalyst obtained can be granulated into extrudates, beads, tablets, granules, or formed into honeycomb blocks or blocks with any suitable shape. According to the present invention, the novel catalyst is prepared according to the following main steps:

(a) Preparation of an intimate mixture of modified titanium dioxide or modified titanium hydroxide with a filler, with or without a binder material. This preparation is performed mechanically with different types of mechanical facilities used for pastes mixing and malaxating. In some cases a definite quantity of water may be introduced into said mixture in order to obtain a homogeneous and shapable dough, but in most cases the amount of water present in titanium hydroxide and filler is enough to prepare a paste with the required properties. In some cases, the paste has to be dried to a certain extent in the process of dough preparation.

(b) The resulted mixture is shaped into extrudates, beads, tablets, honeycombs or into blocks with any desired shape.

( c) The shaped forms obtained above are dried at a temperature in the range of between 50°C-300°C.

(d) The resulted dried forms are calcined at a temperature in the range of between 300°C-800°C.

In the preparation of the mixture of the components according to step (a), the modified titanium dioxide can be used in the form of a titanium hydroxide wet cake as taken from a filter, in the form of partially dried wet cake, or in the form of a completely dried, or calcined material. The filler component may be used also either in the form of a wet cake, partially dried cake, or a completely dried material. The main object of this step is to obtain a mixture possessing the following properties: - a high extent of homogeneity;

- a mixture consistency which should be useful in the step of shaping into desirable granules or blocks, having a high hardness. In many cases the prepared dough forms after the thermal treatment, granules with a high hardness even without using a binder in the stage of dough preparation. When a higher hardness of the granulated material is required, sols of silicic acid may be added during the process up to 20% by weight calculated on the SiO₂ The resulted wet granules may be kept in air for some time or may be put into a drier immediately. Different types of dryers can be used for this purpose and the drying process can be conducted at a wide range of temperatures, such as between the ambient one and up to 300°C. Generally, the wet granules are dried first at 100°C-150°C until the granules become hard enough to be loaded into a calcination kiln at a temperature of about 400°C for about 1 to 10 hours, but sometimes the temperature of calcination may be increased up to 800°C. In order to illustrate the present invention and the advantages thereof, the following Examples are given for a better understanding of the invention, being understood that these Examples have to be considered only as illustrative, without imposing any limitation thereof. The aims of these Examples are to show the advantages of the novel catalyst in comparison with commercial ones in respect to: hardness, thermal and hydrothermal stability, mesopore and macropore structures and a smaller quantity of active component than in the known catalysts but at the same extent of catalytic activity.

Two groups of Examples are shown: in Examples 1 and 2 the catalysts were prepared in a laboratory, while in Examples 4 to 13, the catalysts were prepared in a pilot plant. The Example 3 is presented for comparative purpose.

EXAMPLE 1.

This example demonstrates the preparation of the catalyst with the modified titanium dioxide as an active component, powdery precipitated silica as a filler and silica sol as a binder material, possessing a high catalytic activity in the Claus reaction.

In this example the following starting materials were used:

- Modified titanium dioxide prepared according to Example 1 in the above mentioned copending patent application. - Powdery silica precipitated from a solution of sodium silicate with sulfuric acid.

- An acidic sol of silicic acid.

The modified titanium dioxide and powdery silica were dried at 105°C for 24 hours. After drying, the two materials had losses on ignition values (LOI) as shown in Table 1.

Acidic sol of silicic acid was prepared from sodium sol of silicic acid using a cation exchange resin C-100 produced by PUROLITE™. An amount of 0.5 liter of sodium silica sol with a concentration of about 10% by weight, calculated on anhydrous silica dioxide, had been treated with the H-form of the above mentioned cation exchange resin thus obtaining an acid sol of silicic acid having a pH of about 3.0, the SiO₂ content in the sol being 9.8% by weight.

The above materials were mixed in a laboratory mortar in the form of a paste, its composition calculated on dry basis, is given in Table 2.

The paste was passed through a laboratory extruder obtaining extrudates with a diameter of 3.0 mm. The extrudates were dried at 120°C for 3 hours in a laboratory dryer and then calcined at 400°C for 3 hours in a laboratory muffle. The structural properties of the catalyst obtained are given in Table 3. As can be noticed, the quantity of titanium dioxide present in 1 m³ of catalyst bed, is only 140 Kg which is less than the quantity 777-900 kg present in a commercial catalyst (see Table 5). In order to test the catalytic activity of the above prepared extrudates, these were crushed and the fraction between 8 and 12 mesh was separated by sieving and then tested in a bench scale pilot plant using the conditions as for the Claus process. The results of the tests are given in Table 4. EXAMPLE 2.

This example demonstrates that the modified titanium dioxide can be calcined before its incorporation in the mixture with the other components of the catalyst.

The same modified titanium dioxide as in .Example 1 was preliminary calcined at 350°C for 5 hours.

The paste mixture was prepared from this titanium dioxide, siliceous filler and a binder in a laboratory mortar (see Table 1); the composition of this paste, calculated on dry basis is given in Table 2.

The paste had been formed into the same extrudates as in Example 1 in a laboratory extruder and then the extrudates were dried and calcined as in Example 1. The structural properties of the prepared catalyst are given in Table 3. The extrudates were crushed and the fraction with sizes of crumbs between 8 and 12 mesh, was tested in a bench scale pilot plant using the conditions as for Claus process. The results are given in Table 4.

EXAMPLE 3. (for comparison purposes) An experiment was carried out using a commercial titanium dioxide catalyst.

This catalyst was introduced in the same reactor as in Examples 1 and 2.

The amount of the titanium dioxide used in this case, was substantially the same as in Example 1. According to Table 4 it can be noticed that the difference in carbon disulfide conversion is equal to 10% which shows that the titanium dioxide present in the novel catalyst is more active than the same amount of titanium dioxide present in a commercial catalyst.

EXAMPLES 4- 6.

In the preparation of the catalysts samples in a pilot plant, diatomaceous earth "CELITE FC" received from LOMPOS (USA) was used as an inert filler. The chemical composition of this material was as follows:

% by weight SiO2 85.8 AI2O3 3.8

Fe2O3 1.2

CaO+MgO 1.1

Na2O+K2O 1.1

P2O5 0.2 Loss on ignition 3.6

The physical properties of this material were as follows: Loose weight (g/liter) 120

Oil absorption (% by weight) 128

Water absorption (% by weight) 280 As natural diatomaceous earth contains some undesirable impurities, such as sodium, potassium, iron, aluminum, it was preliminary purified by an acid treatment. For this purpose hydrochloric or sulfuric acid having a concentration of 15%-20% was used, the temperature during this treatment being between 90°-98° C for about 3 hours. The purified diatomaceous earth was filtered, washed with demineralized water and used for the preparation of shapable dough in the form of wet cake or as a dried material. In some cases diatomaceous earth can be used as a filler without a preliminary purification.

In Examples 4, 5 and 6, the purified diatomaceous earth was used . The titanium dioxide from Example 1 in our above mentioned copending patent application was used as an active component in Examples 4-6 using silica hydrogel as a binder material, prepared by the following procedure: Basic silica sol prepared in its sodium form, having an initial concentration of about 3% (calculated as SiO2) was evaporated to an extent that its concentration increased to 20-30% by weight. Then this sol was treated with a cation exchanger in order to eliminate the sodium and accordingly to

10 decrease its pH to about 3.0. The resulted acidic sol was treated with an aqueous solution of ammonia until its pH increased up to 7 and then it was heated. During the heating a coagulation of the sol into hydrogel took place and was used in the mixing with the other components. The modified titanium dioxide in the form of a wet cake, a purified and dry diatomaceous earth and silica hydrogels were mixed in a double shaft mixer-sigma blade (produced by Sepor). After obtaining a homogeneous mixture, it was slightly dried in order to obtain a proper consistency suitable for extrusion. The extrudates having a diameter of 3.6 mm, were obtained with a piston extruder, dried at 120°C for about two hours and calcined at 450 °C for 3 hours.

The losses on ignition are shown in Table 1 , the compositions of the catalysts as prepared in a pilot plant are given in Table 2 and the properties of the catalysts obtained are given in Table 5.

EXAMPLES 7-11

This group of Examples describes the preparation of the novel catalyst in the form of extrudates possessing a high hardness without any binder. In each case the catalyst consists of two components: the modified titanium dioxide (as prepared according to our above mentioned copending patent application) and as an inert filler, a purified diatomaceous earth (as obtained in Examples 4-6). Losses on ignition for the components are shown in Tablel and the compositions of the catalysts are given in Table 2. In each case the active component was mixed with the inert filler and the resulted mixture was malaxated thus producing a shapable dough using a double shaft mixer, as described in Examples 4 to 6 and a piston extruder as used in a process of granulation. After drying at 120°C the extrudates were calcined in a muffle at a temperature of 450° C for 3 hours. The following variations exist between the Examples 7 to 11 : In Example 7, diatomaceous earth was introduced as a wet cake after filtration, containing 35% of dry material. The paste was partially dried to a

11 material containing 55.2% of dry material, which was extrudated using a piston extruder.

In other cases, diatomaceous earth was used in the form of a dried material (120°C) having a loss on ignition between 5%to 6% (see Table 1).

EXAMPLES 12 and 13.

These Examples demonstrate the possibility of obtaining a hard and thermal stable extrudated catalyst, using stabilized commercial titanium dioxides as described in the above mentioned copending patent application and compared with commercial titanium dioxides (Example 12), or its mixture with a precipitated titanium dioxide according to the above mentioned copending patent application (Example 13).

12 TABLE L

Components used for catalysts preparation:

Modified titanium dioxide (active component) Filler Binder

Number of example from our Loss on Name Loss on Name Loss on

Example copending Appln, in which this ignition, ignition, ignition, No T1O2 preparation was descπbed weight % weight % weight %

9 1 Powdery 78 Acidic 90 2 silica silica sol

3 0 78 Acidic 90 2 silica sol

59 2 Diatoma50 Silica 70 3 ceous hydroearth gel

57 5 40 Silica 74 5 hydrogel

52 3 40 Silica 79 5 hydrogel

10 63 7 65 absent

12 62 5 80 absent

70 0 50 absent

10 73 0 40 absent

1 1 6A 72.0 50 absent

12 21 in amount of 37% and 63 0 5.0 absent

22 in amount of 37%(by weight) 59 0

13 21 in amount of 55% and 61 0 50 absent

6 in amount of 15%

13 TABLE 2

Compositions of catalysts prepared in laboratory and in a pilot plant on the basis of precipitated modified titanium dioxides (% by weight calculated on dry basis)

EXAMPLES

LABORATORY PILOT PLANT

1 2 4 5 6 7 8 9 10 11 12 13

Composition

1. Ti02 28.4 28.0 30.0 35.0 35.0 35.0 25.0 40.0 38.0 45.0 74.0 70.0

2.Siliceous component

(calculated as Si0₂) 60.2 61.4 55.0 55.0 55.0 65.0 75.0 60.0 62.0 55.0 26.0 30.0

3. Binder materials: none none none none none none none

3.1 Acidic silica sol 11.4 10.6 none none none

3.2 Silica hydrogel none none 15.0 10.0 10.0

TABLE 3. Structural properties of catalysts prepared in laboratory:

Tamped Specific Composition of 1 m³ of a bulk density, surface area, tamped catalyst bed,

Example No. kg/m^~3 m²g^"1 kg/m^"3

Silica Silica as Titanium as a a binder dioxide filler (from sol)

1 490 134 294 55 140

2 480 137 294 50 134

14 TABLE 4.

Catalytic activity of novel catalysts prepared in laboratory on Claus process.

Example Extent of conversion in reactions

No.

H₂S + SO₂ COS + H₂O CS₂ + H₂O

Initial Aged Initial Aged Initial Aged Catalyst Catalyst² Catalyst Catalyst² Catalyst Catalyst²

1 93¹ 97¹ 100 100 96 90

2 9J¹ 97¹ 100 100 97 91

3 94¹ 86 comparative)

calculated as percentage of conversion at equilibrium state,

² aaggiinngg wwaass ccaarrrried out in a laboratory with a common hydrothermal treating and sulfating.

15 TABLE 5. Properties of catalysts prepared in a pilot plant.

Hardness Specific Tamped Composition of a 1 m³ of tamped (Crushing surface bulk catalyst bed,

Example strength), area, density, kg/m³ No kg/extrudate mV¹ kg/m³

TiO₂ Filler Binder

4 20 165 635 191 349 95

5 17 175 634 222 222 63

6 12 179 567 198 312 57

7 20 174^x 590 207 383 absent

8 12 166^x 597 209 388 absent

9 9 144 545 191 354 absent

10 13 - 617 234 383 absent

11 14 220^x 640 288 352 absent

12 9 164 800 592¹ 208 absent

13 11 187 700 490² 210 absent

Commercial

Claus catalyst based on titanium dioxides

"A" 7 134^x 860 777 - -

"B" 7 124^x 1000 900 - -

Notes:

1. Mixture of stabilized commercial dioxides (see Table 1).

2. Mixture of stabilized commercial titanium dioxide and precipitated titanium dioxide (see Table 1).

3. The sign " means that the values of specific surface area were determined with Coulter instrument SA 3100. Figures without this sign were measured with Analyser 4200 (Leeds and Northrup Instruments). In all Tables the meaning of this sign is as above.

16 TABLE 6.

Adsorption pore volume distribution on pore diameters for the novel catalyst in comparison with the commercial one

Adsorption pore volume formed bv pores with diameter: less than 100 nm greater than 4.1 nm greater than 3.5 nm

Example cc/g In % of the cc/g In % of the cc/g In % of the No. analogous analogous analogous values for the values for the values for the commercial commercial commercial catalyst "A" catalyst "A" catalyst "A"

10 0.33 127 0.31 129 0.32 123

11 0.36 138 0.33 138 0.35 135

Commercial Claus catalyst

"A" 0.26 100 0.24 100 0.26

Note: all the data listed in this table were measured with Coulter Instrument SA 3100.

17 TABLE 7.

Macropore structure of catalysts prepared in a ilot plant in comparison with known ones.

Pore volume formed by macropores with diameter

Example No. greater than indicated (cc/g)

100 nm 200 nm 300 nm 400 nm

Mixture of catalysts from Examples 4, 5 and 6 0.38 0.30 0.20 0.05

Mixture of catalysts from Examples 7, 8 and 9 0.30 0.25 0.20 0.10

Example 10 0.21 0.14 0.05 0.02

Commercial Claus catalysts:

A: 0.16 0.01 - -

B: 0.01 less than 0.01 - -

C: 0.01 less than 0.01 - -

TABLE 8:

Thermal stability of catalysts prepared in a pilot plant in comparison with known Claus catalysts.

Specific Specific surface area of the catalyst calcinated surface area for 3 hours at indicated temperatures, m²g^"1

Example No. of starting catalyst, m²g^"1 500 °C 700 °C 800 °C 900 °C

7 174^x 89 58

10 175 121 109

11 220^x 214 146 122

12 180^x 164 118 79

Commercial Claus catalysts based on Tiθ2:

A 134^x 28 4

B 110 103 43 22 8

C 200 112 46 28 17

18 TABLE 9:

Hydrothermal stability of the novel catalyst in comparison with known ones.

Conditions of the hydrothermal treatment: -temperature: 500 °C, -treating agent: water vapor, -duration: 5 hours:

Specific surface area (mV ) of steamed catalyst, calculated:

Example No. per 1 gram per ^• 1 cc of tamped layer of a catalyst bed

10 120 74 11 135 86 12 113 90

Commercial catalyst "A" based on Tiθ2 66 57

Commercial catalyst "B" based on Tiθ2 59 59

19 TABLE 10.

Catalytic activity of catalysts prepared in a pilot plant

Number Catalytic Type of instalCatalysts from Extent of conversion in of test process lation used for Examples the reactions testing

H₂S+S0₂ COS/CS2 +H20

1 Claus process Bench-scale 7 89 92 pilot plant

2 Sulfreen process Big pilot Mixture of Examples 4,5,6 temperature 220 °C 44 84 temperature 250 °C 38 90

3 Sulfreen process Big pilot Mixture of Examples 7,8,9 temperature 220 °C 44 84 temperature 250 °C 39 92

4 Sulfreen process Big pilot Commercial catalyst "C" temperature 220 °C 43 81 temperature 250 °C 37 84

Note in test 1 the extent of conversion in the reaction H2S+SO2 is calculated as a percentage of conversion at equilibrium state, in the other tests real values of conversion for the reactions H2S+SO2 and COS/CS2+H2O, both are listed

20

Claims

C L A I M S:

1. A novel catalyst composition, based on a modified titanium dioxide as a catalytic active component as described in our copending PCT patent application No. and comprises at least 3% by weight of said catalytic active component, an inert filler selected from siliceous materials and optionally a binder, being characterized by a complex of improved properties, including a high hardness, a developed macropore and mesopore structure, a high thermal stability as measured by a specific surface area up to 130 m²/g for a catalyst composition, comprising 45% by weight of the above mentioned modified titanium dioxide calcined at 800°C for three hours, a high hydrothermal stability, and a high catalytic activity in the Claus reaction, carbonyl sulfide hydrolysis, carbon disulfide hydrolysis and Sulfreen process.

2.The novel catalyst composition according to Claim 1 , being characterized by the high hydrothermal stability as measured by a specific surface area up to 140 m²/g for the above mentioned catalyst composition subjected to a hydrothermal treatment with water vapors at a temperature of 500°C for five hours.

3. The novel catalyst composition according to Claimsl and 2, wherein the developed macropore structure, calculated as pore volume formed by pores having a diameter greater than 200 nm, is up to 0.35 cc/g.

4. The novel catalyst composition according to Claims 1 to 3, being characterized by a developed mesopore structure, wherein the adsorption pore volume formed by pores with a diameter below 100 nm, is up to 0.38 cc/g.

5. The novel catalyst composition according to Claims 1 to 4, possessing a hardness up to 200% for extrudates with a diameter of 3.6 mm, compared with the extrudates having the same diameter, of known

21 commercial catalysts based on titanium dioxide used in the above mentioned processes.

6. The novel catalyst composition according to Claim 1 , wherein said inert filler is diatomaceous earth.

7. The novel catalyst composition according to Claim 1 , wherein said catalyst is granulated in various shapes.

8. The novel catalyst composition according to Claim 1 , wherein the amount of the catalytic active component is at least 3% by weight.

9. The novel catalyst composition according to Claim 1 , wherein the active component is the modified titanium dioxide precipitated as described therein.

10. The novel catalyst composition according to Claim 6, wherein said diatomaceous earth is purified by a treatment with a mineral acid.

11. The novel catalyst composition according to Claim 10, wherein the mineral acid is selected from hydrochloric acid and sulfuric acid.

12. The novel catalyst composition according to Claim 1 , wherein the inert filler is selected from a precipitated silica and silica hydrogel.

13. A method for preparation the novel catalyst composition according to Claims 1 to 4, which comprises the mixing of the active component with an inert filler, optionally with a binder, then malaxating the mixture to a homogeneous and shapable dough which can be produced into extrudates, beads or other shapes.

14. The method for obtaining the novel catalyst composition according to Claim 13, wherein said components can be used in the form of wet cakes or dried materials.

15. The method for obtaining the novel catalyst composition as described in Claims 1 and 4, as a hard, thermal and hydrothermal stable extrudate.

16. The method for obtaining the novel catalyst composition according to Claim 13, wherein said binder is selected from an acid silica sol, basic silica sol and silica hydrogel.

22