Catalyst comprising palladium and silver, and its application for selective hydrogenation

Abstract

Disclosed are a catalyst, its preparation and use in selective hydrogenation, which catalyst has a porous support grain on which are deposited palladium and silver, and at least one alkali and/or alkaline earth metal; the porous support contains a refractory silica, alumina and/or silica-alumina oxide, where at least 80 wt. % of the palladium is distributed in a crust at the periphery of the support, and at least 80 wt. % of the silver is distributed in a crust at the periphery of the support, the local content of palladium at each point along the diameter of the grain follows the same course as the local content of silver.

Description

[0001]The process of selective hydrogenation allows the polyunsaturated compounds in oil cuts to be transformed by conversion of the most unsaturated compounds into the corresponding alkenes while avoiding total saturation and thus the formation of the corresponding alkanes.[0002]The object of the invention is to propose a catalyst and a method for preparing the said catalyst. This catalyst performs very well in processes of selective hydrogenation of the unsaturated hydrocarbon compounds present in hydrocarbon cuts, preferably cuts derived by steam cracking and / or catalytic cracking, and in particular from C3 cuts.PRIOR ART[0003]The catalysts of selective hydrogenation of these cuts are often palladium-based, in the form of small particles of metal deposited on a support which may be a refractory oxide in the form of beads, extrudates or trilobes, or forms having other geometries. The palladium content and the size of the particles of palladium are among the criteria that are impor...

AI Technical Summary

Benefits of technology

[0012]US2010/217052 describes a supported PdAg catalyst, in which the palladium and the silver partially form an alloy in a thin peripheral crust, enabling catalysts to be obtained that are particularly suitable for selective hydrogenation of C2 cuts. The proportion of particles forming an alloy is measured by adsorption of CO onto the catalytic surface. The support used is of a very small surface area (1 to 80 m2/g). The preparation process comprises a step of impregnation of the two metals into a solution containing water and an organic solvent miscible in the water, optional drying, and calcination at a maximum temperature of 400° C. The percentage of water in the impregnation solution allows variation of the thickness of the palladium and silver crust.

[0013]The aim of the present invention is to obtain catalysts having very good performances for the processes of selective hydrogenation of unsaturated hydrocarbon compounds present in the hydrocarbon cuts derived by steam cracking and/or catalytic cracking, and in particular in the C3 cuts.

[0014]The Applicants discovered—and this constitutes the subject of the present invention—that the performances of a bimetallic PdAg crust catalyst could be distinctly improved when the atoms of silver are in close proximity to the palladium atoms within the crust containing the two metals. This is because the thin crust of the catalyst thus comprises palladium and silver arranged in a specific way: the local content of palladium at each point along the diameter of the grain follows the same course as the local content of silver. In other words, when the local content of palladium at a given point alo

Problems solved by technology

These studies further revealed the difficulty in obtaining the desired synergis

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