Abstract: There is provided a method for recycling a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A method for recycling a denitration catalyst includes a step of spraying an aqueous solution with a pH of 7 or more onto a used denitration catalyst while the denitration catalyst is set in a denitration device to remove a surface of the denitration catalyst. The denitration catalyst contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m2/g or more. The denitration catalyst after recycling is used for denitration at 200° C. or lower.

Abstract: There is provided a method for recycling a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A method for recycling a denitration catalyst includes a step of removing a used denitration catalyst from a denitration device and then coating the used denitration catalyst with a catalyst component. The catalyst component contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m2/g or more, and the denitration catalyst after recycling is used for denitration at 200° C. or lower.

Abstract: Disclosed herein is a system for generating a carbon dioxide gas stream that includes an absorber, a regenerator that lies downstream of the absorber, a carbon dioxide wash station that lies downstream of the regenerator and a reverse osmosis system for receiving a wash solution from the carbon dioxide wash station.

Abstract: Processes for fatty acid ketonization and alcohol dehydration, wherein an alumina catalyst disposed in, or removed from, a reaction zone may be regenerated by contacting the catalyst with steam during or after a coke oxidizing step. In an embodiment, such processes may provide C2-C43 alkenes. In another embodiment, such processes may provide C11-C43 ketones, which can be deoxygenated to give saturated hydrocarbons, unsaturated hydrocarbons, and mixtures thereof. Base oils and transportation fuels may be produced via such processes.

Abstract: Methods of removing iron from a catalytic converter having an accumulation of one or more iron compounds and regenerating a catalytic converter are provided. A catalytic converter having an accumulation of one or more iron compounds embedded or deposited thereon can be treated with a substantially aqueous alkaline solution in which the substantially aqueous alkaline solution includes an antioxidant.

Abstract: A hydrocarbon selective catalytic reduction (HC-SCR) catalyst is regenerated using a nitrogen-based reductant agent. The HC-SCR catalyst is in communication with a power system such as an internal combustion engine and receives exhaust gasses from the internal combustion engine. Sulfur in the exhaust gasses may deactivate the HC-SCR catalyst by sulfur oxides forming thereon. To remove the sulfur oxides, a nitrogen-based reductant agent is introduced to the exhaust gasses. The nitrogen-based reductant agent decomposes to nitrogen oxides and hydrogen. The hydrogen reacts with the sulfur oxides to form hydrogen sulfides thereby removing the sulfur oxides from the HC-SCR catalyst.

Abstract: A process for regenerating one or more deactivated cobalt comprising Fischer-Tropsch catalyst particle(s), comprising the steps of: (i) oxidizing the catalyst particle(s) at a temperature between 20 and 400° C.; (ii) treating the catalyst particle(s) for more than 5 minutes, (iii) drying the catalyst particle(s); and (iv) optionally reducing the catalyst particle(s) with hydrogen or a hydrogen comprising gas. This process may be preceded by a step in which Fischer-Tropsch product is removed from the catalyst particle(s). The treatment is performed using carbon dioxide and a liquid comprising ammonia.

Abstract: We provide a process and apparatus for preparing a used catalyst for disposal, comprising: a. hydrolyzing a used ionic liquid catalyst comprising an anhydrous metal halide to produce a hydrolyzed product; and b. separating the hydrolyzed product into a liquid phase and a solid phase; wherein the liquid phase comprises a non-water-reactive aqueous phase and a hydrocarbon phase; and wherein the solid phase comprises a solid portion of the hydrolyzed product, that is not water reactive. A vessel is used for the hydrolyzing and a separator is used for the separating.

Abstract: A method of re-using a spent fluid catalytic cracking (FCC) catalyst, previously used in an FCC process, in an additional FCC process, where the method includes the steps of: providing FCC catalyst that has been utilized in an FCC process, defined as spent FCC catalyst, wherein the spent FCC catalyst includes both aluminum and at least one rare earth element therein; and reacting the spent FCC catalyst with an extracting agent to extract at least a portion of the at least one rare earth element from the spent FCC catalyst, while extracting no more than half of the aluminum from the spent FCC catalyst. After performing the reacting step, the reacted spent FCC catalyst can be used in an additional FCC process.

Abstract: Disclosed is an electrode catalyst comprising: (a) a support; (b) metal catalyst particles supported on the support and formed of a catalytically active metal or metal-containing alloy; and (c) an anti-coarsening compound, which is dispersed in at least one region selected from the group consisting of interstitial spaces among the catalyst particles and contact sites between the support and the catalyst particles, and has a coarsening temperature higher than that of the catalyst. A method for preparing the electrode catalyst is also disclosed.

Abstract: A process for regenerating one or more deactivated cobalt comprising Fischer-Tropsch catalyst particle(s), comprising the steps of: (i) oxidizing the catalyst particle(s) at a temperature between 20 and 400° C.; (ii) treating the catalyst particle(s) for more than 5 minutes with a solvent, which solvent comprises an amine, (iii) drying the catalyst particle(s); and (iv) optionally reducing the catalyst particle(s) with hydrogen or a hydrogen comprising gas. This process may be preceded by a step in which Fischer-Tropsch product is removed from the catalyst particle(s).

Abstract: The present disclosure relates to methods for treating deactivated SCR catalysts having an increased SO2/SO3 conversion rate as a result of the accumulation of one or more iron compounds. The methods are characterized in that the catalysts are treated with an aqueous solution of an acidic reactive salt or hydrogen fluoride, with the addition of at least one antioxidant.

Abstract: A process for regenerating Raney catalysts by treating the catalyst with liquid ammonia with a water content of less than 5% by weight and with hydrogen having a partial pressure of 0.1 to 40 MPa in the temperature range from 50 to 350° C. for at least 0.1 hour.

Abstract: A process is provided for producing a complex oxide catalyst which exhibits superior catalytic activity in a vapor phase catalytic oxidation reaction, particularly in production of unsaturated aldehyde and unsaturated carboxylic acid. The process is characterized by the steps of preparing an aqueous slurry by mixing a complex oxide containing molybdenum and cobalt with an acid and water; drying the aqueous slurry; and calcining the resulting dried solid. Preferably, the complex oxide is obtained as follows: a molybdenum- and cobalt-containing complex oxide catalyst which has been used in a vapor phase catalytic oxidation reaction is mixed with an aqueous extracting solution obtained by dissolving at least one of ammonia and an organic base in water, to thereby extract molybdenum and cobalt into the aqueous phase; and the aqueous phase is dried and is then calcined under an atmosphere of an oxidizing gas.

Abstract: A method and apparatus is provided for regenerating a sorbent that has been poisoned by components derived from flue gas. The sorbent is treated with an agent to remove the poisoning components and introduce a promoting agent into the sorbent. The method and apparatus can also be used to enhance the effectiveness of a new sorbent.

Abstract: A process for regenerating one or more deactivated cobalt comprising Fischer-Tropsch catalyst particle(s), comprising the steps of: (i) oxidising the catalyst particle(s) at a temperature between 20 and 400° C.; (ii) treating the catalyst particle(s) for more than 5 minutes, (iii) drying the catalyst particle(s); and (iv) optionally reducing the catalyst particle(s) with hydrogen or a hydrogen comprising gas. This process may be preceded by a step in which Fischer-Tropsch product is removed from the catalyst particle(s). The treatment is performed using carbon dioxide and a liquid comprising ammonia.

Abstract: The instant invention provides a process for improving catalytic activity of catalyst systems for reductive amination of aliphatic cyanoaldehydes to aliphatic diamines. The process for improving catalytic activity of catalyst systems for reductive amination of aliphatic cyanoaldehydes to aliphatic diamines comprises the steps of: (1) feeding ammonia, optionally hydrogen, and optionally one or more solvents over one or more heterogeneous metal based catalyst systems having a reduced catalytic activity for a period of greater than 1 hour at a temperature in the range of from 50° C. to 500° C.; wherein said one or more heterogeneous metal based catalyst systems have a yield of less than 90 percent based on the molar conversion of cyanoaldehydes to diamines; and (2) thereby improving the catalytic activity of said one or more heterogeneous metal based catalyst systems.

Abstract: An in-situ method for regenerating a deactivated catalyst removes a calcium sulfate layer masking active catalyst sites. A reducing agent converts the calcium sulfate to calcium oxide, which is then removed, by reintrainment into the flue gas steam using soot blowers or sonic horns. The method is particularly useful for regenerating selective catalytic reduction (SCR) catalysts used to remove nitrogen oxides from flue gas produced by combustion of coal from the Powder River Basin. The method can be practiced using existing SCR system hardware, and without removing the SCR system from service.

Abstract: Provided is a process for safely transporting or recycling an ionic liquid catalyst based on chloroaluminates. The process comprises mixing a secondary alcohol with an ionic liquid based on a chloroaluminate and allowing a reaction to occur forming an aluminum chloride adduct precipitate. The precipitate is filtered and the secondary alcohol removed, leaving a solid salt. This solid salt is the ionic liquid catalyst absent aluminum chloride, for example, Nbutylpyridinium chloride. This salt is recycled to the reactor. AlCl3 is added to the salt prior to introduction into the reactor to remake the ionic liquid catalyst, for example, Nbutylpyridinium heptachloroaluminate.

Abstract: A process for regenerating one or more deactivated cobalt comprising Fischer-Tropsch catalyst particle(s), comprising the steps of: (i) oxidising the catalyst particle(s) at a temperature between 20 and 400° C.; (ii) treating the catalyst particle(s) for more than 5 minutes with a solvent, which solvent comprises an amine, (iii) drying the catalyst particle(s); and (iv) optionally reducing the catalyst particle(s) with hydrogen or a hydrogen comprising gas. This process may be preceded by a step in which Fischer-Tropsch product is removed from the catalyst particle(s).

Abstract: The invention pertains to a process for activating an hydrotreating catalyst comprising a Group VIB metal oxide and a Group VIII metal oxide which process comprises contacting the catalyst with an acid and an organic additive which has a boiling point in the range of 80-500° C. and a solubility in water of at least 5 grams per liter (20° C., atmospheric pressure), optionally followed by drying under such conditions that at least 50% of the additive is maintained in the catalyst. The hydrotreating catalyst may be a fresh hydrotreating catalyst or a used hydrotreating catalyst which has been regenerated.

Abstract: A process for extractively removing homogeneously dissolved catalysts from a reaction effluent of a hydrocyanation of unsaturated mononitriles to dinitriles with a hydrocarbon H, including performing the steps of a) concentrating the reaction effluent before step b) by distillation at pressures of from 0.1 to 5000 mbar and temperatures of from 10 to 150° C., b) adding a hydrocarbon H to the concentrated reaction effluent to obtain a stream I, and c) feeding stream I, without prior separation of the liquid phases, into an extraction apparatus and extracting it at a temperature T with the hydrocarbon H to obtain a stream II comprising the hydrocarbon H enriched with the catalyst and a stream III having a low catalyst content.

Abstract: A process for converting fine catalyst slurried in heavy oil into a coke-like material from which catalytic metals can be recovered comprises mixing fine catalyst slurried in heavy oil with solvent, which causes asphaltenes in the heavy oil to precipitate from the heavy oil; separating fine catalyst and precipitated asphaltenes from the heavy oil and solvent; and converting precipitated asphaltenes to a coke-like material by pyrolizing fine catalyst and precipitated asphaltenes separated from the heavy oil.

Abstract: A process for removing metal halides from regenerated ionic liquid catalyst comprising interacting a regenerated ammonium-based metal-halide ionic liquid catalyst or an ammonium-based metal-halide ionic liquid catalyst undergoing regeneration with either the parent ammonium halide salt from which the ionic liquid catalyst was made or a corresponding mixed salt having an ammonium halide to metal halide molar ratio of 0 to less than 2.0 is disclosed.

Abstract: A process for regenerating one or more deactivated cobalt comprising Fischer-Tropsch catalyst particle(s) in situ in a reactor tube, said process comprising the steps of: (i) oxidising the catalyst particle(s) at a temperature between 20 and 400° C.; (ii) treating the catalyst particle(s) for more than 5 minutes with a solvent, (iii) drying the catalyst particle(s); and (iv) optionally reducing the catalyst with hydrogen or a hydrogen comprising gas. This process may be preceded by a step in which Fischer-Tropsch product is removed from the catalyst particle(s).

Abstract: [Problem] Provided is a method for regenerating a catalyst, the method decreasing the SO2 oxidation rate, which has been increased by Fe and V compounds, of a spent denitration catalyst to an extremely low level, and improves the oxidation activity of the catalyst for metal mercury by the regeneration treatment. [Solving Means] A method for regenerating a catalyst, including steps of immersing a spent denitration catalyst composed mainly of titanium oxide in (a) a mixed aqueous solution containing phosphate ions and oxo-acid ions of one or more elements selected from vanadium (V), molybdenum (Mo), and tungsten (W), (b) a heteropoly acid compound aqueous solution containing phosphorus and one or more elements selected from V, M, and W, or (c) a mixed aqueous solution containing a phosphate compound and a vanadyl compound, and then drying the catalyst.

Abstract: A catalyst for the production of methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum is regenerated by a method comprising the steps of drying a mixture containing a deactivated catalyst, an ammonium ion, a nitrate ion and water, molding the dried mixture, firstly calcining the molded product in an atmosphere of an oxidizing gas at a temperature of 360 to 410° C., and then secondly calcining the product in an atmosphere of a non-oxidizing gas at a temperature of 420 to 500° C. The regenerated catalyst has substantially the same catalytic activity as a fresh catalyst in a gas phase catalytic oxidation reaction of methacrolein, isobutylaldehyde, isobutane or isobutyric acid to prepare methacrylic acid.

Abstract: A catalyst for the production of methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum is regenerated by a method comprising the steps of heat-treating a mixture containing a deactivated catalyst, water, a nitrate ion and an ammonium ion having a molar ratio to the nitrate ion of 1.3 or less at a temperature of at least 100° C., drying the mixture to obtain a dried catalyst, and calcining the dried catalyst. The regenerated catalyst has substantially the same catalytic activity as a fresh catalyst in a gas phase catalytic oxidation reaction of methacrolein, isobutylaldehyde, isobutane or isobutyric acid to prepare methacrylic acid.

Abstract: A catalyst for the production of methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum is regenerated by a method comprises the steps of heat-treating a deactivated catalyst at a temperature of at least 350° C., mixing the deactivated catalyst with water, a nitrate ion and an ammonium ion, then drying the mixture to obtain a dried catalyst, and calcining the dried catalyst.

Abstract: A method of modifying an alkylation catalyst to reduce the formation of condensed hydrocarbon species thereon. The method comprises providing an alkylation catalyst comprising a plurality of active sites. The plurality of active sites on the alkylation catalyst may include a plurality of weakly acidic active sites, intermediate acidity active sites, and strongly acidic active sites. A base is adsorbed to a portion of the plurality of active sites, such as the strongly acidic active sites, selectively poisoning the strongly acidic active sites. A method of modifying the alkylation catalyst by providing an alkylation catalyst comprising a pore size distribution that sterically constrains formation of the condensed hydrocarbon species on the alkylation catalyst or by synthesizing the alkylation catalyst to comprise a decreased number of strongly acidic active sites is also disclosed, as is a method of improving a regeneration efficiency of the alkylation catalyst.

Abstract: A process for removing metal halides from regenerated ionic liquid catalyst comprising interacting a regenerated ammonium-based metal-halide ionic liquid catalyst or an ammonium-based metal-halide ionic liquid catalyst undergoing regeneration with either the parent ammonium halide salt from which the ionic liquid catalyst was made or a corresponding mixed salt having an ammonium halide to metal halide molar ratio of 0 to less than 2.0 is disclosed.

Abstract: The invention is directed to a method of rejuvenating silicoaluminophosphate molecular sieve catalyst that has been deactivated hydrothermally as well as a method of using the rejuvenated catalyst to make an olefin product from an oxygenate feed. In particular, the invention is directed to rejuvenating the catalyst by contacting it with warm water, ammonium salts, dilute acids or low pressure steam until the catalytic activity level of the catalyst has been increased to the desired extent.

Abstract: The invention is directed to a method of rejuvenating silicoaluminophosphate molecular sieve catalyst that has been deactivated hydrothermally as well as a method of using the rejuvenated catalyst to make an olefin product from an oxygenate feed. In particular, the invention is directed to rejuvenating the catalyst by contacting it with warm water, ammonium salts, dilute acids or low pressure steam until the catalytic activity level of the catalyst has been increased to the desired extent.

Abstract: A process for economically separating and recovering valuable metal components, with few kinds of chemicals being used, with no waste water that causes environmental pollution being discharged, and also perfectly no by-products being formed by means of simple steps.

Abstract: A process for the regeneration of a zeolitic catalyst which is at least partially exhausted by use in the synthesis of optionally substituted methylenedianiline (MDA) and derivatives thereof, or of a mixture of optionally substituted MDA and derivatives thereof, with a higher homologous product the process involving washing said catalyst with an aromatic compound having at least one substitutent on the aromatic ring having activating characteristics with respect to the electrophilic substitution, in liquid or at least partially liquid phase.

Abstract: Process for the recovery of perfluorinated sulphonic acid from a hydrocarbon residue, comprising the steps of (a) treating the residue with an alkyl ammonium salt of the perfluorinated sulphonic acid or a mixture of an alkyl ammonium salt of the perfluorinated sulphonic acid and the perfluorinated sulphonic acid in an amount being effective to liquefy the residue at ambient temperature; (b) contacting the liquefied residue with water at conditions to obtaining an aqueous extract containing the perfluorinated sulphonic acid and/or the alkyl ammonium salt of the perfluorinated acid into water; and (c) separating water from the aqueous extract to recover the perfluorinated sulphonic acid or the mixture of the acid and the ammonium salt.

Abstract: The present invention provides a process for regenerating a spent aromatics alkylation or transalkylation catalyst comprising a molecular sieve by contacting the spent catalyst with an oxygen-containing gas at a temperature of about 120 to about 600° C. and then contacting the catalyst with an aqueous medium, such as an ammonium nitrate solution, an ammonium carbonate solution or an acid solution.

Abstract: A process for the preparation of a catalyst support material involving the steps of: (a) subjecting a used titania-on-silica catalyst to a decoking treatment, (b) washing the decoked catalyst with a washing liquid selected from an aqueous solution of a mineral acid, an aqueous solution of an ammonium salt and combinations thereof, and (c) drying and calcining the washed and decoked catalyst to yield the catalyst support material. The support material thus obtained is suitably used as support material for titania in a heterogeneous catalyst for the epoxidation of olefins into alkylene oxides.

Abstract: The present invention relates to the effective utilization of a used catalyst containing at least molybdenum, an A element (at least one element selected from the group consisting of phosphorus and arsenic) and an X element (at least one element selected from the group consisting of potassium, rubidium and cesium), and provides a process for producing a catalyst, which comprises dispersing said used catalyst in water, adding thereto an alkali metal compound and/or ammonia solution, adjusting the resulting mixture to pH 6.5 or less to generate a precipitate containing at least molybdenum and the A element, and using the precipitate as a material for catalyst-constituting elements.

Abstract: The invention provides a method for regenerating with high efficiency a deteriorated catalyst of reduced activity, said catalyst originating from a heteropolyacid catalyst containing heteropolyacid formed of molybdophosphoric acid and/or molybdovanadophosphoric acid, or a salt thereof, to a heteropolyacid catalyst which exhibits approximately equivalent activity level to that of the fresh catalyst. Said method comprises mixing a deteriorated catalyst and a nitrogen-containing heterocyclic compound under the conditions whereunder ammonium ions and nitrate anions are present at such ratio that the amount of total ammonium ions per mol of total nitrate anions does not exceed 1.7 mols, drying the mixture and calcining the same.

Abstract: A catalyst active in ammonia synthesis with improved activity and a process for the recovery of useful components from the catalyst.

Abstract: A process is described for regenerating exhausted zeolitic catalysts containing titanium and deriving from oxidation processes of organic substrates with hydrogen peroxide. Said process consists in carrying out a treatment in an aqueous medium with hydrogen peroxide in the presence of inorganic fluorinated compounds, subsequent to thermal treatment of the exhausted catalyst.

Abstract: This invention relates to a process for reactivating a dehydrocyclodimerization catalyst. Dehydrocyclodimerization catalysts which contain an aluminum phosphate binder can be deactivated when they are exposed to hydrogen at temperatures above 500° C. The instant process restores substantially all of the catalyst's lost activity. The process involves treating the catalyst with a fluid comprising water and drying the catalyst. The process is employed particularly advantageously in combination with coke removal for reactivating catalysts that contain coke deposits and that have also been hydrogen deactivated. This invention also relates to a method of producing a dehydrocyclodimerization catalyst that is resistant to hydrogen deactivation.

Abstract: This invention provides a method for the regeneration of a denitration catalyst which comprises cleaning a denitration catalyst having reduced denitration power with an aqueous alkaline solution to remove the substances deposited thereon, and subjecting the catalyst to an activation treatment with an aqueous acid solution; a method for the regeneration of a denitration catalyst which comprises cleaning a denitration catalyst having reduced denitration power with a cleaning fluid comprising an aqueous solution containing sulfuric acid or ammonia at a concentration of 0.05 to 20% by weight and maintained at a temperature of 10 to 90°C.; and a method for the regeneration of a denitration catalyst which comprises cleaning a denitration catalyst having reduced denitration power under the above-described conditions, and impregnating the denitration catalyst with a catalytically active component so as to support it on the catalyst.

Abstract: The present invention provides a process for regenerating a spent aromatics alkylation or transalkylation catalyst comprising a molecular sieve by contacting the spent catalyst with an oxygen-containing gas at a temperature of about 120 to about 600° C. and then contacting the catalyst with an aqueous medium, such as an ammonium nitrate solution, an ammonium carbonate solution or an acetic acid solution.

Abstract: The invention provides a method for regenerating with high efficiency a deteriorated catalyst of reduced activity, said catalyst originating from a heteropolyacid catalyst containing heteropolyacid formed of molybdophosphoric acid and/or molybdovanadophosphoric acid, or a salt thereof, to a heteropolyacid catalyst which exhibits approximately equivalent activity level to that of the fresh catalyst. Said method comprises mixing a deteriorated catalyst and a nitrogen-containing heterocyclic compound under the conditions whereunder ammonium ions and nitrate anions are present at such ratio that the amount of total ammonium ions per mol of total nitrate anions does not exceed 1.7 mols, drying the mixture and calcining the same.

Abstract: Disclosed are a self-catalytic bath and a method for the deposition of Ni—P alloy on a substrate. The bath comprises nickel sulfate, sodium hypophosphite as a reducing agent, acetic acid as a buffer and traces of lead as a stabilizer. It also includes a citrate used as a complexing agent associated with a gluconate used both as a catalyst and a stabilizer. The disclosed bath makes it possible to tolerate large quantities of hypophosphite and is relatively long-lived. Furthermore, it can be used to prepare large quantities of Ni—P alloy per liter of solution.

Abstract: This invention provides a method for the regeneration of a denitration catalyst which comprises cleaning a denitration catalyst having reduced denitration power with an aqueous alkaline solution to remove the substances deposited thereon, and subjecting the catalyst to an activation treatment with an aqueous acid solution; a method for the regeneration of a denitration catalyst which comprises cleaning a denitration catalyst having reduced denitration power with a cleaning fluid comprising an aqueous solution containing sulfuric acid or ammonia at a concentration of 0.05 to 20% by weight and maintained at a temperature of 10 to 90°C.; and a method for the regeneration of a denitration catalyst which comprises cleaning a denitration catalyst having reduced denitration power under the above-described conditions, and impregnating the denitration catalyst with a catalytically active component so as to support it on the catalyst.

Abstract: A catalyst for preparing aldehydes by hydroformylation of olefins or olefinically unsaturated compounds comprising at least one rhodium compound and a non-aqueous ionic ligand liquid of the formula (Q.sup.+).sub.a A.sup.a-, where Q.sup.+ is a singly charged quaternary ammonium and/or phosphonium cation or the equivalent of a multiply charged ammonium and/or phosphonium cation and A.sup.a- is a sulfonated triarylphosphine.

Abstract: The invention features a method for treating a supported catalyst with a sulphur compound based active phase and a mercury compound contaminated mineral support. This method consists in implementing the following steps: the said catalyst is contacted with a basic aqueous solution of at least one sulphide selected among alkaline metal sulphides, alkaline-earth metal sulphides or ammonium sulphide; then the catalyst is separated from the basic aqueous solution. At the end of this process, the treated catalyst shows the same characteristics as before its contamination by mercury.