Catalytic hydrodechlorination of trichloromethane

Abstract

Use of a catalyst comprising a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, for the hydrodechlorination of trichloromethane, the catalyst being selected from: (i) a Pt-Mo / Al2O3 catalyst, where the carrier is alumina (Al2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo); (ii) a Pt-Ag / Al2O3 catalyst, where the carrier is alumina (Al2O3), the active metal is platinum (Pt), and the second metal is silver (Ag); (iii) a Pt-Co / Al2O3 catalyst, where the carrier is alumina (Al2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or (iv) an Ir / SiO2 catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

Description

[0001] 378.0861 PC

[0002] HYDRODECHLORINATION CATALYST

[0003] Technical field

[0004] The present invention is directed to new hydrodechlorination catalysts, and in particular, to new hydrodechlorination catalysts that enable the selective hydrodechlorination of trichloromethane (CHCI3) into dichloromethane (CH2CI2).

[0005] Background

[0006] Industrially, chloromethanes (i.e., carbon tetrachloride (CCI4), trichloromethane (CHCI3), dichloromethane (CH2CI2), and chloromethane (CH3CI)) are typically produced by reacting methane (CH4) with chlorine (Cl2). The chlorination reaction proceeds via a low-selectivity radical mechanism, meaning that the products stream includes a mixture of the four possible chloromethanes.

[0007] As market conditions can vary, there is a need for production processes that exhibit a high degree of flexibility, such that the composition of the chloromethane products stream can be optimized. Currently, the higher chloromethanes (i.e., CCI4and CHCI3) are the least desired in the market. Because of this, their economic value is lower, and in some cases these compounds are seen as undesired and incinerated.

[0008] In response, the catalyzed reaction of CCI4with H2to CHCI3and HCI (also called hydrodechlorination) has been studied and some suitable catalysts have been developed. These are commonly based on noble metals platinum (Pt) and palladium (Pd), with activated carbon, alumina (AI2Os), or silica (SiO2) as carriers.

[0009] The analogous hydrodechlorination reaction of CHCI3into CH2CI2is more challenging and has been less investigated. However, CH2CI2is a useful solvent for many chemical processes. It is also used in the food industry to decaffeinate coffee and tea, and as a blowing agent for polyurethane foams.

[0010] Accordingly, there is a need for a reaction that can convert CHC into CH2CI2(and CH3CI and / or CH4). 378.0861 PC

[0011] Summary of the Disclosure

[0012] In a first aspect, the present invention is directed to the use of a catalyst comprising a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, for the hydrodechlorination of trichloromethane, the catalyst being selected from:

[0013] (i) a Pt-Mo / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo);

[0014] (ii) a Pt-Ag / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is silver (Ag);

[0015] (iii) a Pt-Co / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or

[0016] (iv) an I r / SiO2catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

[0017] Advantageously, the use of a Pt-Mo / AI2O3catalyst, a Pt-Ag / AI2O3catalyst, a Pt-Co / AI2O3catalyst, or an lr / SiO2catalyst, in accordance with the first aspect of the invention, has been found to enable surprisingly selective hydrodechlorination of trichloromethane with hydrogen into dichloromethane. Furthermore, these catalysts can be easily produced using wetness impregnation methods and have been found to exhibit excellent stability during the hydrodechlorination reaction. The use of these catalysts in accordance with the first aspect of the invention therefore provides a flexible, economic, and long-term route to the lower chloromethanes in response to external market dynamics.

[0018] In a second aspect, the invention provides a process for producing dichloromethane, chloromethane and / or methane from trichloromethane, the process comprising, under an oxygen- free atmosphere: in a reducing stage, contacting a catalyst with a hydrogen-containing gas stream at a temperature of from 250 to 400 °C, preferably 300 to 350 °C, thereby forming a reduced catalyst; and in a reaction stage, contacting the reduced catalyst with a trichloromethane-containing gas stream at a temperature of from 100 to 350 °C, wherein the catalyst comprises a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, and is selected from:

[0019] (i) a Pt-Mo / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo);

[0020] (ii) a Pt-Ag / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is silver (Ag); 378.0861 PC

[0021] (iii) a Pt-Co / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or

[0022] (iv) an I r / SiO2catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

[0023] As shown in the Examples below, this Pt-Mo / AI2O3, Pt-Ag / AI2O3, Pt-Co / AI2O3, or lr / SiO2catalysed hydrodechlorination reaction provides a highly selectivity and highly productive route to dichloromethane. The process therefore offers a less costly and more environmentally friendly outlet for trichloromethane.

[0024] Figures

[0025] Figure 1 is a schematic diagram of the catalytic performance testing used in the Examples.

[0026] Detailed description

[0027] The various aspects of the present invention will be elucidated further below.

[0028] As indicated above, in a first aspect, the present invention is directed to the use of a catalyst comprising a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, for the hydrodechlorination of trichloromethane, the catalyst being selected from:

[0029] (i) a Pt-Mo / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo);

[0030] (ii) a Pt-Ag / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is silver (Ag);

[0031] (iii) a Pt-Co / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or

[0032] (iv) an I r / SiO2catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

[0033] The catalyst may have a total metal loading (i.e., the total amount of active metal and second metal present in the catalyst) of from 0.5 to 3.0 wt.%, based on the total weight of the catalyst. Preferably, the total metal loading of the catalyst is from 0.7 to 2.5 wt.%, and more preferably of from 0.8 to 2.1 wt.%, based on the total weight of the catalyst. The metal loading of the catalyst can be measured, for example, by inductively coupled plasma-optical emission spectroscopy (ICP-OES). 378.0861 PC When the catalyst is a Pt-Mo / AI2O3catalyst, it may contain from 0.7 to 1 .3 wt.% Pt and from 0.1 to 1 .0 wt.% Mo, based on the total weight of the catalyst. Preferably, the Pt-Mo / AI2O3catalyst contains from 0.8 to 1 .2 wt.% Pt and from 0.2 to 0.7 wt.% Mo, and more preferably from 0.9 to 1.1 wt.% Pt and from 0.3 to 0.6 wt.% Mo, based on the total weight of the catalyst.

[0034] When the catalyst is a Pt-Ag / AI2O3catalyst, it may contain Pt and Ag in a molar ratio of from 5:1 to 1 :5. Preferably, the Pt-Ag / AI2O3catalyst contains Pt and Ag in a molar ratio of from 3:1 to 1 :3, more preferably of from 2.5:1 to 1 :1 , and most preferably of from 2:1 to 1 .5:1 .

[0035] When the catalyst is a Pt-Co / AI2O3catalyst, it may contain from 0.7 to 1 .3 wt.% Pt and from 0.1 to 2.0 wt.% Co, based on the total weight of the catalyst. Preferably, the Pt-Co / AI2O3catalyst contains from 0.8 to 1 .2 wt.% Pt and from 0.2 to 0.7 wt.% Co, and more preferably from 0.9 to 1.1 wt.% Pt and from 0.3 to 0.6 wt.% Co, based on the total weight of the catalyst.

[0036] When the catalyst is an I r / SiO2catalyst, it may contain from 0.8 to 2.1 wt.% Ir, based on the total weight of the catalyst. Preferably, the lr / SiO2catalyst contains from 0.8 to 1 .6 wt.% Ir, more preferably from 0.8 to 1 .4 wt.% Ir, based on the total weight of the catalyst.

[0037] When the active metal supported on the carrier is platinum, the Pt particles may have an average particle size of less than 10 nm, as determined by electron microscopy. Preferably the Pt has an average particle size of less than 5 nm, and more preferably less than 2 nm. Smaller particles are used to increase the activity of the catalyst. The Pt particles may have a minimum average particle size of 1 nm, as determined by electron microscopy.

[0038] When a second metal is supported on or added to the carrier, the second metal (Mo, Ag or Co) may have an average particle size of less than 2 nm, as determined by electron microscopy. Preferably, the Mo, Ag or Co particles have an average size of less than 1 nm, and more preferably less than 0.5 nm. Again, smaller particles are chosen to provide increased activity of the catalyst.

[0039] When the catalyst carrier is alumina, either an alpha phase alumina or a gamma phase alumina may be used. Preferably, the alumina carrier is gamma phase alumina. The alumina carrier may have a primary particle size less than 100 nm as determined by electron microscopy, and / or a Brunauer-Emmett-Teller (BET) surface area greater than 150 m2 / g, preferably greater than 160 m2 / g. Preferably, the purity of the alumina carrier is above 95 wt.%, preferably above 98 wt.% and more preferably above 99 wt.% (on trace metals basis). 378.0861 PC When the catalyst carrier is silica, it may have a primary particle size less than 100 nm as determined by electron microscopy, and / or a Brunauer-Emmett-Teller (BET) surface area greater than 150 m2 / g, preferably greater than 180 m2 / g, and more preferably greater than 200 m2 / g.

[0040] The I r / SiO2catalyst may be prepared using a wetness impregnation method, followed by drying and calcining. The impregnation method involves deposition of the active components (i.e., the active metal and optional second metal) on the carrier surface by means of their liquid solution (where an excess of active solution is used). For the Pt-Co / AI2O3, Pt-Mo / AI2O3and Pt-Ag / AI2O3catalysts, a sequential wetness impregnation method may be used. Here, deposition of Mo, Co, or Ag onto the alumina carrier by means of their liquid solution is first performed to prepare a Mo-, Co-, or Ag-modified alumina carrier, which can be subsequently dried and calcined. Deposition of Pt on the Mo-, Co-, or Ag-modified carrier surface may then be carried out (again, followed by drying and calcining). For the Pt-Ag / AI2O3catalysts, it can be advantageous to limit light exposure during preparation. The catalysts, once made, are preferably pelletized and sieved to yield pellet sizes of from 75 to 212 pm.

[0041] The present invention is further directed to a process for producing dichloromethane, chloromethane and / or methane from trichloromethane, the process comprising, under an oxygen- free atmosphere: in a reducing stage, contacting a catalyst with a hydrogen-containing gas stream at a temperature of from 250 to 400 °C, preferably 300 to 350 °C, thereby forming a reduced catalyst; and in a reaction stage, contacting the reduced catalyst with a trichloromethane-containing gas stream at a temperature of from 100 to 350 °C, wherein the catalyst comprises a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, and is selected from:

[0042] (i) a Pt-Mo / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo);

[0043] (ii) a Pt-Ag / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is silver (Ag);

[0044] (iii) a Pt-Co / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or

[0045] (iv) an I r / SiO2catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

[0046] The process is performed under an oxygen-free atmosphere. For the avoidance of doubt, the term “an oxygen-free atmosphere” is used herein to mean an atmosphere containing less than 1 vol% oxygen. The process is run under an oxygen-free atmosphere to help keep Pt in metallic 378.0861 PC state. Preferably, the process is also run under anhydrous conditions. For the avoidance of doubt, the term “anhydrous” is used herein to mean containing as little water as possible. Anhydrous conditions are advantageous to avoid sintering of the Pt nanoparticles. For this reason, the catalysts should be dry. The anhydrous conditions and oxygen-free atmosphere useful for the process can be obtained, for example, by using inert gases (such as nitrogen, argon and / or helium), in the hydrogen-containing and trichloromethane-containing gas streams. The process is preferably performed under ambient pressure.

[0047] In the reducing stage, the catalyst is reduced under H2flow, using a temperature of from 250 to 400 °C, preferably 300 to 350 °C to allow the reduction of the active metal. The optimum temperature for reducing each catalyst can be found using Temperature-Programmed Reduction with H2(H2-TPR). The hydrogen-containing gas stream may contain at least 10 vol% H2in an inert gas. Preferably, the hydrogen-containing gas stream contains at least 15 vol% H2in helium, more preferably at least 20 vol% H2in helium. The total flow rate of the hydrogen-containing gas stream may be at least 100 mL / min.

[0048] In the reaction stage, the reduced catalyst is contacted with a trichloromethane-containing gas stream at a temperature of from 100 to 350 °C. The trichloromethane-containing gas stream may comprise hydrogen and trichloromethane in a molar ratio of at least 10:1 . Preferably, the trichloromethane-containing gas stream comprises hydrogen and trichloromethane in a molar ratio of at least 15:1 , more preferably at least 20:1 , and most preferably at least 40:1. The trichloromethane-containing gas stream may also comprise inert gases (such as nitrogen, argon and / or helium). The total flow rate of the trichloromethane-containing gas stream may be at least 50 mL / min.

[0049] The reaction stage may be advantageously carried out at a temperature of from 120 to 220 °C, preferably of from 150 to 200 °C. When the catalyst is a Pt-Mo / AI2O3 catalyst, the reaction stage is preferably carried out at a temperature of from 160 to 200 °C, preferably of from 170 to 190 °C, more preferably of from 175 to 185 °C, and most preferably at 180 °C. When a Pt-Ag / AI2O3catalyst is used, the reaction stage is preferably carried out at a temperature of from 130 to 170 °C, preferably of from 140 to 160 °C, more preferably of from 145 to 155 °C, and most preferably at 150 °C. When the catalyst is an lr / SiO2catalyst, the reaction stage is preferably carried out at a temperature of from 170 to 210 °C, preferably of from 180 to 200 °C, more preferably of from 185 to 195 °C, and most preferably at 190 °C. It has been found that each catalyst has a different optimum temperature range in which the highest selectivity towards dichloromethane is seen.

[0050] Preferably, the process of the present invention further includes: 378.0861 PC in a separating stage, separating the dichloromethane from the chloromethane and / or methane.

[0051] In the separating stage, the dichloromethane may be separated from the chloromethane and / or methane by distillation. After separation, the process preferably has a dichloromethane productivity above 500 mmol • gCat-1• h-1, preferably above 600 mmol • gCat-1• h-1, more preferably above 700 mmol • gCat-1• h-1, and most preferably above 800 mmol • gCat-1• h-1.

[0052] It is noted that various elements of the present invention, including but not limited to preferred ranges for the various parameters, can be combined unless they are mutually exclusive.

[0053] The invention will be elucidated by the following examples without being limited thereto or thereby.

[0054] Examples

[0055] Preparation of the Pt-Mo / AI2O3catalysts

[0056] The Pt-Mo / AI2O3catalysts were prepared using a sequential wetness impregnation method. The Pt metal loading in all cases was fixed at 1 .0 wt.%, while the Mo loading was varied to obtain the designated amount.

[0057] Taking the preparation of the Pt-0.5Mo / AI2O3 catalyst as an example, 0.5 mL of an ammonium molybdate tetrahydrate ((NH4)6Mo7O24-4H2O, 99.0 % (metals basis), Merck) aqueous solution (10 mg / mL of Mo content) and 0.99 g y-AI2O3(>99 % (metals basis), Fisher Scientific) were added to a glass vial containing 3 mL distilled water at room temperature, and the mixture was subjected to water evaporation at 120 °C until a slurry-like product was formed. The slurry was then dried overnight at 80 °C and subsequently calcined in static air at 550 °C for 4 hours. Next, 1 mL of a dihydrogen hexachloroplatinate(IV) hexahydrate (H2PtCI6-6H2O 99.95% (metals basis), Pt 37.5% min, Thermo Fisher Scientific) aqueous solution (10 mg / mL of Pt content) was added to an aqueous solution containing the Mo-modified y-AI2O3, obtained in the previous step (0.99 g Mo-modified y-AI2O3in 2 mL water). The water was again evaporated at 120 °C until a slurry was obtained, followed by an overnight drying process at 80 °C. Finally, the composite underwent calcination at 400 °C for 4 h. 378.0861 PC

[0058] Preparation of the Pt-Co / AI2O3catalysts

[0059] The Pt-Co / AI2O3catalysts were prepared using a sequential wetness impregnation method. The Pt metal loading in all cases was fixed at 1 .0 wt.%, while the Co loading was varied to obtain the designated amount.

[0060] Taking the preparation of the Pt-0.5Co / AI2O3catalyst as an example, 0.5 mL of a cobalt(ll) nitrate hexahydrate (Co(NO3)2-6H2O, ACS reagent, >98%, Merck) aqueous solution (10 mg / mL of Co content) and 0.99 g y-AI2O3(>99 % (metals basis), Fisher Scientific) were added to a glass vial containing 3 mL distilled water at room temperature, and the mixture was subjected to water evaporation at 120 °C until a slurry-like product was formed. The slurry was then dried overnight at 80 °C and subsequently calcined in static air at 550 °C for 4 h. Next, 1 mL of a dihydrogen hexachloroplatinate(IV) hexahydrate (H2PtCle-6H2O 99.95% (metals basis), Pt 37.5% min, Thermo Fisher Scientific) aqueous solution (10 mg / mL of Pt content) was added to an aqueous solution containing the Co-modified y-AI2O3, obtained in the previous step (0.99 g Co-modified y-AI2O3in 2 mL water). The water was again evaporated at 120 °C until a slurry was obtained, followed by an overnight drying process at 80 °C. Finally, the composite underwent calcination at 400 °C for 4 h.

[0061] The Pt-Ag / AI2O3catalysts were prepared using a sequential wetness impregnation method. The total amount of the metal loading was kept at 1 .0 wt.%.

[0062] Taking the preparation of the Pt5oAg5o / AI203catalyst as an example, 0.356 mL of a silver nitrate (AgNO3, ACS, 99.9+% (metals basis), Thermo Fisher Scientific) aqueous solution (10 mg / mL of Ag content), and 0.99 g of y-AI2O3(> 99 % (metals basis), Fisher Scientific) were added to a glass vial containing 3 mL distilled water at room temperature. The glass vial was then covered by aluminum foil and the mixture was subjected to water evaporation at 90 °C until a slurry-like product formed. The slurry was then dried overnight at 80 °C and subsequently calcined in static air at 400 °C for 4 h. Next, 0.644 mL of a dihydrogen hexachloroplatinate(IV) hexahydrate (H2PtCI6-6H2O, 99.95% (metals basis), Pt 37.5% min, Thermo Fisher Scientific) aqueous solution (10 mg / mL of Pt content) was added to an aqueous solution containing the Ag-modified y-AI2O3, obtained in the previous step (0.994 g Ag-modified y-AI2O3in 2 mL water). The water was again evaporated at 90 °C until a slurry was obtained, followed by an overnight drying process at 80 °C. Finally, the composite underwent calcination at 400 °C for 4 h. 378.0861 PC

[0063] Preparation of the I r / SiO2catalyst

[0064] The I r / SiO2catalysts were prepared using a wetness impregnation method.

[0065] 0.99 g of the SiO2support (CARiACT Q-10, Fuji Silysia Chemical, Ltd.) was dispersed in 3 mL deionized water, and 1 mL of a dihydrogen hexachloroiridate(IV) hydrate (H2lrCI6-xH2O, 99 % (metals basis), Ir 38-42%, Thermo Fisher Scientific) aqueous solution (10 mg / mL of Ir content) was added. The solution was subsequently evaporated at 120°C until a slurry-like product was obtained. After drying at 80 °C overnight, the sample was calcined at 400 °C for 4 h.

[0066] Preparation of the Pt / AI2O3catalyst

[0067] The Pt / AI2O3catalyst was prepared using a wetness impregnation method. The Pt metal loading was fixed at 1 .0 wt.%.

[0068] 0.99 g of the y-AI2O3support (> 99 % (metals basis), Fisher Scientific) was dispersed in 3 mL deionized water, and 1 mL of a dihydrogen hexachloroplatinate(IV) hexahydrate (H2PtCl6‘6H2O, 99.95 % (metals basis), Pt 37.5% min, Thermo Fisher Scientific) aqueous solution (10 mg / mL of Pt content) was added. The solution was subsequently evaporated at 120°C until a slurry-like product was obtained. After drying at 80 °C overnight, the sample was calcined at 400 °C for 4 h.

[0069] Preparation of Pt / SiO2catalyst

[0070] The Pt / SiO2catalyst was prepared using a wetness impregnation method. The Pt metal loading was fixed at 1 .0 wt.%.

[0071] 0.99 g of the SiO2support (CARiACT Q-10, Fuji Silysia Chemical, Ltd.) was dispersed in 3mL deionized water, and 1 mL of a dihydrogen hexachloroplatinate(IV) hexahydrate (H2PtCI6-6H2O, 99.95 % (metals basis), Pt 37.5% min, Thermo Fisher Scientific) aqueous solution (10 mg / mL of Pt content) was added. The solution was subsequently evaporated at 120°C until a slurry-like product was obtained. After drying at 80 °C overnight, the sample was calcined at 400 °C for 4 h.

[0072] Catalyst characterisation of the Pt / AI2O3and Pt-Mo / AI2O3catalyst

[0073] Specific surface area 378.0861 PC N2adsorption isotherms were performed at -196 °C on a Sync 400 (3P Instruments) instrument. Prior to the measurement, samples were dried under vacuum at 150 °C for 12 h. For each measurement, a liquid N2bath was employed to maintain the temperature at -196 °C.

[0074] Specific surface areas were calculated using the Brunauer-Emmett-Teller (BET) method, wherein the isotherm data within a relative pressure (p / p0) range of 0.05-0.25 were adopted. Total pore volumes were calculated based on the absorbed N2volume at a relative pressure of approximately 0.99.

[0075] The results showed there to be no difference in total pore volume between the freshly prepared Pt / AI2O3 and Pt-Mo / AI2O3 catalysts.

[0076] Chemical composition

[0077] Inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements were conducted to analyze the chemical composition of the catalyst materials, using a SPECTRO CIROSCCDinstrument (SPECTRO Analytical Instruments). The samples for ICP-OES were prepared by dissolving the solid materials in aqua regia.

[0078] The results showed the Pt and Mo loadings to be in excellent agreement with the amount of the Pt and Mo precursor used.

[0079] Temperature-programmed reduction with H2

[0080] Temperature-programmed reduction with H2(H2-TPR) was performed by using an AMI-300IP instrument (Altamira Instruments) equipped with a thermal conductivity detector (TCD) to determine the consumption of H2, and hence to determine the most suitable temperature for reducing the catalyst. The catalyst sample (approximately 60 mg) was placed in a U-shaped quartz reactor between two plugs of quartz wool and underwent a 30-minute pretreatment at 120 °C to remove water. The analysis was conducted in 5 vol% H2in Ar (25 mL min-1) atmosphere by heating up the catalyst from 50 °C to 800 °C at a rate of 10 °C min-1.

[0081] Element and particle size distribution

[0082] High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was performed on the Spectra300 electron microscope at 200 kV. All samples were prepared by dispersing pre-reduced fresh and spent Pt / AI2O3 and Pt-Mo / AI2O3 catalyst powders onto lacey carbon-coated copper grids. The corresponding elemental mapping was measured to analyze 378.0861 PC the element distribution of samples on the same instrument using energy-dispersive spectroscopy (EDS). The particle size distribution of the catalysts was analyzed over 200 nanoparticles using the Imaged software.

[0083] HAADF-STEM images reveal the presence of individual Pt atoms, few-atom Pt ensembles, and Pt nanoclusters distributed on both Y-AI2O3and Mo-modified Y-AI2O3supports. The size of Pt nanoparticles shows no remarkable difference among these catalysts (~1 nm on average).

[0084] The EDS elemental mapping of Pt-Mo / AI2O3sample unambiguously illustrates a highly uniform dispersion of Pt and Mo on the y-AI2O3substrate.

[0085] Catalytic Performance Test

[0086] Before catalytic testing, all catalyst powders were pelletized and sieved to yield pellet sizes of from 75 to 212 pm.

[0087] The catalyst material was then reduced under conditions found to be optimum by the temperature-programmed reduction with H2, discussed above. For this, 200 mg of catalyst material was packed between two quartz wool plugs inside a quartz tube, heated to 300 °C at 5 °C / min and reduced under 20 vol% H2in He flow (total flow rate: 100 mL / min) at 300 °C for 2 h. Subsequently, the gas flow was switched to He (80 mL / min), allowing the reactor to cool to 120 °C.

[0088] Hydrodechlorination reactions were then evaluated at ambient pressure in a continuous-flow fixed-bed reactor consisting of a quartz tube with an internal diameter of 7 mm. H2(Linde 5.0), He (Linde 5.0), and N2(Linde 5.0, internal standard) were regulated with a set of digital mass flow controllers (Bronkhorst) to obtain the desired feed speed, and liquid CHCI3was supplied by a syringe pump (LEGATO 100, KD Scientific) to a vaporizer unit operated at 100 °C. All lines were heated at 120 °C to avoid any condensation. The inlet gas was composed of 2 vol% CHCI3, 40 vol% H2, 8 vol% N2, and 50 vol% He, and it was supplied at a constant flow rate of 50 mL / min. The effluent gas from the reactor was analyzed with an online custom build Trace 1300 gas chromatograph (GO) equipped with two flame ionization detectors (Fl Ds) and two thermal conductivity detectors (TCDs). After GO analysis, the gas stream was passed through three washing bottles in series (first two filled with water and the last one filled with 4M NaOH) for neutralization before releasing in the ventilation system.

[0089] For each catalyst, ramp experiments were performed prior to performance testing to preselect the reaction temperature. In these ramp experiments, the initial reaction temperature was held at 378.0861 PC 120 °C for 60 min before gradually increasing to 300 °C at a heating rate of 1 °C / min. The effluent gas was analyzed by GC every 5 min and the temperature at which the CHCh conversion was above 90%, or at which the best CH2CI2 yield was obtained, was preselected.

[0090] For the performance test, the catalyst was subjected to the mixture gas consisting of 2 vol% CHCI3, 40 vol% H2, 8 vol % N2, and 50 vol% He at the preselected temperature and held for 6 h.

[0091] The above testing method is illustrated schematically in Figure 1 . Here: 5 is an evaporator, 6 is a fixed-bed reactor and 7 is a gas chromatograph. In the process, e.g., for Pt-0.5Mo / AI2O3, the catalyst material is packed between two quartz wool plugs inside the fixed bed reactor 6. The reactor 6 is heated to 300 °C while hydrogen gas and helium gas are flowed through, via supply lines 1 and 3, respectively. After 2 hours, the gas flow is switched to helium and the reactor (and the reduced catalyst material) is allowed to cool to 120 °C. The reactor 6 is heated back up to 180 °C and the gas flow switched to a trichloromethane-containing gas stream containing predetermined quantities of hydrogen gas (supplied via 1), nitrogen gas (supplied via 2), helium gas (supplied via 3), and vaporised trichloromethane (supplied via 4 and evaporator 5, operated at 100 °C). The reaction is monitored via gas chromatograph 7. After analysis, the gas stream is neutralised before release, by passing through wash bottles 8, 9 and 10 (8 and 9 being filled with water and 10 being filed with 4M NaOH).

[0092] Example 1 : Catalytic performance in hydrodechlorination of CHCI3of Pt / AI2O3and Pt-Mo / AI2O3catalysts

[0093] In this example, the catalytic performance of Pt / AI2O3was compared to three Pt-Mo / AI2O3catalysts with different Mo loadings (specifically, 0.3 wt.%, 0.5 wt.%, and 0.8 wt.%, based on the total weight of the catalyst). The Pt metal loading in all cases was fixed at 1 .0 wt.%, based on the total weight of the catalyst.

[0094] Each catalyst was tested using the Catalytic Performance Test described above. The preselected reaction temperature was 180 °C. The results can be seen in Table 1 .

[0095] Table 1: Catalytic performance in hydrodechlorination of CHCI3 at 180 °C 378.0861 PC The results show that the introduction of Mo to a Pt / AI2O3catalyst significantly increases the selectivity and production of CH2CI2. For example, the selectivity and productivity of CFhCbover Pt-0.5Mo / AI2O3catalyst are 2.6 times higher than those achieved by Pt / AI2O3catalyst. Furthermore, when Mo is added in an amount of 0.3 wt.% to 0.5 wt.%, the same CHCI3conversion is also achieved.

[0096] Example 2: Catalytic performance in hydrodechlorination of CHCI3of Pt / AI2O3and Pt-Aq / AI2O3catalysts

[0097] In this example, the catalytic performance of Pt / AI2O3was compared to three Pt-Ag / AI2O3catalysts with different Pt / Ag molar ratios (specifically, 75 / 25, 67 / 33, and 50 / 50). The total metal loading in all cases was fixed at 1 .0 wt.%, based on the total weight of the catalyst.

[0098] Each catalyst was tested using the Catalytic Performance Test described above. The preselected reaction temperature was 150 °C. The results can be seen in Table 2.

[0099] Table 2: Catalytic performance in hydrodechlorination of CHCI3 at 150 °C

[0100] The results show the synergistic effect between Pt and Ag in CHCI3hydrodechlorination reaction over Pt-Ag / AI2O3catalysts. Introducing Ag not only increases the catalytic activity in CHCI3hydrodechlorination but also enhances the selectivity for CH2CI2. The Pt67Ag33 / AI2O3catalyst showed the greatest CHCI3conversion rate and CH2CI2productivity, which were 1 .3 and 2.8 times higher than that of single Pt / AI2O3, respectively.

[0101] Example 3: Catalytic performance in hydrodechlorination of CHCI3of Pt / AI?O3and Pt-Co / AI?O3catalysts

[0102] In this example, the catalytic performance of Pt / AI2O3was compared to three Pt-Co / AI2O3catalysts with different Co loadings (specifically, 0.5 wt.%, 1 .0 wt.%, and 2.0 wt.%, based on the total weight of the catalyst). The Pt metal loading in all cases was fixed at 1 .0 wt.%, based on the total weight of the catalyst.

[0103] Each catalyst was tested using the Catalytic Performance Test described above. The preselected reaction temperature was 180 °C. The results can be seen in Table 3. 378.0861 PC

[0104] Table 3: Catalytic performance in hydrodechlorination of CHCh at 180 °C

[0105] The results show that the introduction of 0.5 wt.% Co to a Pt / AI2O3catalyst significantly increases the selectivity and production of CH2CI2. Here, the selectivity and productivity of CH2CI2over Pt- 0.5CO / AI2O3catalyst are almost double that achieved by Pt / AI2O3catalyst.

[0106] Example 4: Catalytic performance in hydrodechlorination of CHC of Pt / SiO2 and I r / Si O2 catalysts

[0107] In this example, the catalytic performance of Pt / SiO2was compared to lr / SiO2. The total metal loading in all cases was fixed at 1 .0 wt.%, based on the total weight of the catalyst.

[0108] Each catalyst was tested using the Catalytic Performance Test described above. The preselected reaction temperature was 190 °C. The results can be seen in Table 4.

[0109] Table 4: Catalytic performance in hydrodechlorination of CHCb at 190 °C

[0110] The results show that the I r / SiO2catalyst exhibits improved activity in CHCI3hydrodechlorination (94% conversion of CHCI3) and CH2CI2selectivity (58%) over the Pt / SiO2catalyst.

[0111] Example 5: Effect of temperature on catalytic performance in hydrodechlorination of CHCh

[0112] In this example, the catalysts Pt / AI2O3, Pt / SiO2, 1 r / SiO2, Pt-0.5Mo / AI2O3, and Pt67Ag33 / AI2O3were tested at different reaction temperatures using the Catalytic Performance Test described above. The results can be seen in Table 5.

[0113] Table 5: Catalytic performance at different temperatures 378.0861 PC

[0114] The results show that the Pt67Ag33 / AI2O3 catalyst exhibited the lowest T90 (the temperature at 90% CHCh conversion and a criterion for evaluating catalytic activity). For the Pt67Ag33 / AI2O3catalyst, this high conversion can also be seen to result in a higher yield of CH2CI2as compared to the Pt / AI2O3catalyst.

[0115] Example 6: Catalyst stability in hydrodechlorination of CHCh

[0116] In this example, the long-term performance (stability) of the catalysts Pt-0.3Mo / AI2O3and Pt6oAg4o / AI203was tested using the Catalytic Performance Test described above. The testing time and reaction temperature used can be seen in Table 6.

[0117] Table 6: Long-term catalytic performance 378.0861 PC The results show that both Pt-0.3Mo / AI2O3and Pt6oAg4o / AI203have excellent stability during the hydrodechlorination of trichloromethane, showing only minimal deactivation after 600 or 100 hours of operation, respectively.

[0118] Example 7: Effect of different second metals on catalytic performance in hydrodechlorination of CHCI3of Pt / AI O3catalysts

[0119] In this example, the catalytic performance of Pt / AI2O3catalysts with different second metals supported on or added to the alumina carrier were compared. The Pt metal loading in all cases was fixed at 1 .0 wt.%, based on the total weight of the catalyst, while the second metal loading was fixed at 0.5 wt.%.

[0120] Each catalyst was prepared using a sequential wetness impregnation method (as described above for the Pt-Mo / AI2O3catalysts) and tested using the Catalytic Performance Test. The preselected reaction temperature was 180 °C. The results can be seen in Table 7.

[0121] Table 7: Catalytic performance of Pt-based catalysts with different second metals

[0122] The results show that the introduction of Mo or Co to a Pt / AI2O3catalyst significantly increases the selectivity and production of CH2CI2, whereas the introduction of Cr, Mn, Ba or W has little positive effect on either.

[0123] Whilst the invention has been described with reference to an exemplary embodiment, it will be appreciated that various modifications are possible within the scope of the invention.

[0124] In this specification, unless expressly otherwise indicated, the word ‘or’ is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator ‘exclusive or’ which requires that only one of the conditions is met. The word ‘comprising’ is used in the sense of ‘including’ rather than to mean ‘consisting of’. All prior teachings acknowledged above are hereby incorporated by reference. No acknowledgement of 378.0861 PC any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Europe or elsewhere at the date hereof.

Claims

1. 378.0861 PCCLAIMS:1 . Use of a catalyst comprising a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, for the hydrodechlorination of trichloromethane, the catalyst being selected from:(i) a Pt-Mo / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo);(ii) a Pt-Ag / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is silver (Ag);(iii) a Pt-Co / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or(iv) an I r / SiO2catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

2. A use as claimed in claim 1 , wherein the catalyst has a total metal loading of from 0.5 to 3.0 wt.%, preferably of from 0.7 to 2.5 wt.%, and more preferably of from 0.8 to 2.1 wt.%, based on the total weight of the catalyst.

3. A use as claimed in claim 1 or claim 2, wherein the Pt-Mo / AI2O3catalyst contains from 0.7 to 1 .3 wt.% Pt and from 0.1 to 1 .0 wt.% Mo, preferably from 0.8 to 1 .2 wt.% Pt and from 0.2 to 0.7 wt.% Mo, and more preferably from 0.9 to 1 .1 wt.% Pt and from 0.3 to 0.6 wt.% Mo, based on the total weight of the catalyst.

4. A use as claimed in claim 1 or claim 2, wherein the Pt-Ag / AI2O3catalyst contains Pt and Ag in a molar ratio of from 5:1 to 1 :5, preferably of from 3:1 to 1 :3, more preferably of from 2.5:1 to 1 :1 , and most preferably of from 2:1 to 1 .5:1 .

5. A use as claimed in claim 1 or claim 2, wherein the Pt-Co / AI2O3catalyst contains from 0.7 to 1 .3 wt.% Pt and from 0.1 to 2.0 wt.% Co, preferably from 0.8 to 1 .2 wt.% Pt and from 0.2 to 0.7 wt.% Co, and more preferably from 0.9 to 1 .1 wt.% Pt and from 0.3 to 0.6 wt.% Co, based on the total weight of the catalyst.

6. A use as claimed in any preceding claim, wherein the Pt has an average particle size of less than 10 nm, preferably less than 5 nm, and more preferably less than 2 nm, as determined by electron microscopy.378.0861 PC7. A use as claimed in any preceding claim, wherein Mo, Co or Ag has an average particle size of less than 2 nm, preferably less than 1 nm, and more preferably less than 0.5 nm, as determined by electron microscopy.

8. A use as claimed in any preceding claim, wherein the alumina carrier is gamma phase alumina.

9. A use as claimed in any preceding claim, wherein the alumina carrier has a Brunauer- Emmett-Teller (BET) surface area greater than 150 m2 / g, preferably greater than 160 m2 / g.

10. A use as claimed in any preceding claim, wherein the silica and / or alumina carrier has a primary particle less than 100 nm as determined by electron microscopy.11 . A process for producing dichloromethane, chloromethane and / or methane from trichloromethane, the process comprising, under an oxygen-free atmosphere: in a reducing stage, contacting a catalyst with a hydrogen-containing gas stream at a temperature of from 250 to 400 °C, preferably 300 to 350 °C, thereby forming a reduced catalyst; and in a reaction stage, contacting the reduced catalyst with a trichloromethane- containing gas stream at a temperature of from 100 to 350 °C, wherein the catalyst comprises a carrier, an active metal supported on the carrier, and an optional second metal supported on or added to the carrier, and is selected from:(i) a Pt-Mo / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is molybdenum (Mo);(ii) a Pt-Ag / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is silver (Ag);(iii) a Pt-Co / AI2O3catalyst, where the carrier is alumina (AI2O3), the active metal is platinum (Pt), and the second metal is cobalt (Co); or(iv) an lr / SiO2catalyst, wherein the carrier is silica (SiO2), and the active metal is iridium (Ir).

12. A process as claimed in claim 1 1 , wherein the trichloromethane-containing gas stream comprises hydrogen and trichloromethane in a molar ratio of at least 10:1 , preferably at least 15:1 , more preferably at least 20:1 , and most preferably at least 40:1 .

13. A process as claimed in claim 1 1 or 12, wherein the reaction stage is carried out at a temperature of from 120 to 220 °C, preferably of from 150 to 200 °C.378.0861 PC14. A process as claimed in any of claims 11 to 13, further comprising: in a separating stage, separating the dichloromethane from the chloromethane and / or methane, preferably by distillation.

15. A process as claimed in any of claims 1 1 to 14, having a dichloromethane productivity above500 mmol • gCat-1• h-1, preferably above 600 mmol • gCat-1• h-1, more preferably above 700 mmol • gCat-1• h’1, and most preferably above 800 mmol • gCat-1• h’1.

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