AlPO₄‐Supported nickel catalysts. IV.‐Substituent effects in competitive hydrogenation of styrene and its α‐methyl derivative

Styrene (S) and its α‐methyl derivative (MS) were competitively hydrogenated over a series of nickel catalysts supported on the AlPO 4 , AlPO 4 ‐Al 2 O 3 and AlPO 4 ‐SiO 2 systems, using methanol as solvent, under initial hydrogen pressure in the range 0.4‐0.6 MPa and temperatures between 288 and 323 K, obtaining the relative reactivities R MS,S and the relative adsorption constants K MS,S . The R MS,S and K MS,S values were less than unity in the range 0.04‐0.08 indicating that S was adsorbed more strongly and less hindered on these catalysts than MS. With respect to the influence of temperature and pressure on competitive hydrogenation, the relative reactivity R MS,S was found to be independent of the initial hydrogen pressure while the changes of R MS,S with temperature followed and Arrhenius‐type law below a temperature limit. This limit, as well as the slopes and intercepts of the representation log R MS,S vs. T −1 , depended on the supports.