The selective hydrogenation of acetylene over a Ni/SiO2 catalyst in the presence and absence of carbon monoxide

The effect of carbon monoxide on the selective hydrogenation of acetylene over a 2% Ni/SiO2 catalyst at temperatures below 100 °C has been investigated. The product distribution is constant over a wide range of conversions. In the absence of carbon monoxide approximately two-third of the acetylene which reacts is converted to C2 products with an ethane to ethylene ratio of 1:2. The addition of carbon monoxide lowers activity, with a kinetic order of −0.2, decreases the selectivity to C2 products and decreases the extent of ethane formation. These trends are consistent with a parallel reaction scheme in which CO lowers the availability of hydrogen on the nickel surface. Further hydrogenation of product ethylene to ethane, which is intrinsically much faster than that of acetylene, is minimal for acetylene conversions below 99%. However, it does occur with feeds containing excess ethylene. The catalyst shows slow, continuous deactivation during repeated reactions. The deactivation is not due to migration of nickel, as would be expected if Ni(CO)4 was formed. It is associated with the build-up of carbonaceous matter in amounts greatly exceeding the number of surface nickel atoms but less than that known to cause loss of activity through blockage of pores.

Carbon monoxide is shown to have several effects on the selective hydrogenation of acetylene over a Ni/SiO2 catalyst. It inhibits conversion, decreases the yield of C2 products in total and retards hydrogenation of ethylene to ethane. The changes are consistent with literature information concerning the relative strengths of adsorption of the species present in the system.Figure optionsDownload high-quality image (33 K)Download as PowerPoint slide