Distribution effects of supported metals in exothermic hydrogenation

Supported metals are well-recognized commercial catalysts for important industrial selective hydrogenation. Intrinsic catalysis based on structure–function relationship has traditionally been regarded as a main factor to determine hydrogenation selectivity, while the intense heat release in a strong exothermic reaction also inevitably deteriorates the selectivity by causing coke deposition and/or over-hydrogenation. Herein, this work demonstrates a distribution effect by homogeneously dispersing catalytically-active metal particles on oxide support to enhance the selectivity of exothermic hydrogenation. The catalytically-active metal particles with varied dispersion homogeneity, NiCu here, exhibit similar intrinsic catalysis in the intensely exothermic hydrogenation of α-methylstyrene to cumene. However, a distribution effect is found that the increase in metal dispersion homogeneity leads to enhanced cumene selectivity while decreased isopropylcyclohexane (IPCH) selectivity, with a cumene selectivity of > 99 % achieved at a α-methylstyrene conversion of > 99 %. The high selectivity is attributed to the in-situ thermal dissipation caused decrease in temperature increment detected at the catalyst bed, while even a slight temperature increase at catalyst bed could be induced by a large temperature rise at catalytic sites. Benefiting from the lowered temperature increment, the over-hydrogenation to IPCH with a higher activation energy has been inhibited.