Research progress on structure and properties of selective hydrogenation catalyst

The selectivity of hydrogenation catalyst is directly related to the adsorption form of intermediate products on the catalyst surface. By studying the adsorption characteristics of Pd sites, the relationship between the features of Pd active central crystal surface, morphology, structure and catalyst performance is established, which provides an important reference for the research and development of Pd catalysts.

The influence of the type of crystal surface of the active center on the selectivity and activity of catalyst is a hot topic. Li Dianqing synthesized highly dispersed Pd nanoparticles with controllable shape by LDH precursor method, the tetrahedral particles with complete Pd (111) surface showed higher selectivity in selective hydrogenation of acetylene. In addition, Pd nanowires and cubic octahedrons with controllable morphology were prepared in ethylene glycol system, and their effects on selective hydrogenation catalytic reactions were studied. The results showed that Pd nanowires with more crystal surface boundaries showed good activity in selective hydrogenation of acetylene, while Pd cubic octahedrons showed better ethylene selectivity.

Moon studied the effect of Pd particle morphology on selective hydrogenation of acetylene under atmospheric pressure.Different from the above conclusions, the catalytic activity and selectivity of Pd particles with a surface of (100) are better than those of the spherical particles with a surface of (111).  The authors suggest that the selectivity is mainly due to the weak adsorption of C2 species by multiple adsorption sites in the (100) planar structure.

Schoenbaun used two kinds of thiolate (C18 and AT, respectively) to perform controlled enrichment on Pd/Al2O3 surfaces to study the relationship between the modified active sites and the reaction properties. There is only one adsorption form of CO AT the surface active site modified by C18,  there are two adsorption forms of CO at the active site modified by AT.  In the acetylene hydrogenation reaction, the reaction speed of the latter is 17 times that of the former, in the acetylene hydrogenation reaction, the properties of the two active sites are similar.

In addition, the sensitivity of Pd nanoparticles to the hydrogenation structure of 1, 3-butadiene showed that the free radical intermediates generated on the surface of 1, 3-butadiene particles were affected by particle size,  the small size (1~2nm) particles with low coordination sites could promote the production of total hydrogenation product butane.