Doping effects of B in ZrO2 on structural and catalytic properties of Ru/B-ZrO2 catalysts for benzene partial hydrogenation

The B-doped ZrO2 (B-ZrO2) samples with different B/Zr ratios were synthesized using zirconium oxychloride and boric acid as the precursors. Their crystallographic phase retained as tetragonal ZrO2 after the doping of B; however, the amount of the Lewis acid sites increased from 46.1 μmolNH3 g−1 on ZrO2 to 100.6 μmolNH3 g−1 on B-ZrO2(1/10) with the nominal B/Zr molar ratio of 1/10. The Ru/B-ZrO2 catalysts were then prepared by chemical reduction, and their electronic and structural properties were systematically characterized by spectroscopic techniques. It is identified that the Ru nanoparticles (NPs) supported on these B-ZrO2 samples exhibited similar size, chemical state, and microstructure. In the partial hydrogenation of benzene, the turnover frequency of benzene was linearly proportional to the amount of the acid sites on the supports, whereas the selectivity toward cyclohexene displayed a volcanic evolution passing through a maximum of 88% on the Ru/B-ZrO2(1/15) catalyst. Kinetic analysis indicated that the acid sites improved the rate constants of the benzene to cyclohexene step (k1) and the cyclohexene to cyclohexane step (k2) to different degrees. The resulting k1/k2 ratio increased from 3.7 × 10−2 l mol−1 (Ru/ZrO2) to 4.8 × 10−2 l mol−1 (Ru/B-ZrO2(1/15)), and then declined to 4.1 × 10−2 l mol−1 (Ru/B-ZrO2(1/10)), which explained the volcanic evolution of the selectivity toward cyclohexene with respect to the acid amount.