Direct thermal reduction of Ni/Hβ and its improved catalytic performance with stability in hydroalkylation of benzene

The acidic molecular sieve carrier Hβ supported non-noble metal catalyst Ni/Hβ was prepared by equal volume impregnation method and applied to the hydroalkylation of benzene to cyclohexylbenzene. The effects of calcination procedures on the particle size of Ni and the dispersion degree of metal on the carrier were investigated. Compared with the samples reduced by hydrogen after calcination, the active site Ni of Ni/Hβ obtained by direct thermal reduction in hydrogen is mainly dispersed on the surface of the carrier, with better metal dispersion and smaller particle size of Ni. Under the optimized reaction conditions, the initial pressure of H₂ is 2.5 MPa, the amount of catalyst is 4% of the total reaction liquid, and at the reaction temperature 190 °C for 3 h, the conversion of benzene is 38.4%, the selectivity of cyclohexylbenzene is 72.8%, the selectivity of cyclohexane is 5.2%, the selectivity of dicyclohexylbenzene is 16.5%, and the selectivity of other by-products decreased to 5.5%. After the catalyst was reused for 5 times, the conversion of benzene and selectivity of cyclohexylbenzene were both have a slight decrease. Characterization results showed that the structure of the recovered catalyst was stable, but the specific surface area and pore volume decreased significantly, the resulted problem of catalyst pore blockage can be restored through calcination treatment.