Hierarchical molecular sieve-based Ce-Ru oxide for enhanced catalytic oxidation of chlorobenzene: Insight into the synergistic effect of Ce and Ru, the role of molecular sieve

In this work, a series of hierarchical molecular sieve were synthesized via adjusting the ratio of Si/Al. Then, Ce and Ru were supported on the molecular sieve and the loading amount of Ru were optimized. Catalytic evaluation showed that 5Ce0.5Ru/HZ-3 with the value Si/Al ratio of 80 performed the best catalytic activity of chlorobenzene oxidation with T50 and T90 values of 238 ℃ and 278 ℃, respectively and no chlorobenzene conversion can be seen on the 5Ce/HZ-3 and HZ-3, indicating that Ru was the active sites on 5Ce0.5Ru/HZ-3 and Ce played a promoter role in chlorobenzene oxidation. Catalytic stability showed that 5Ce0.5Ru/HZ-3 can maintain the complete conversion of chlorobenzene oxidation at 300°C for 190 h and the CO2 and HCl selectivity kept around 80% and 27%, respectively, while 5Ce0.5Ru performed worse catalytic stability and no HCl was detected. Subsequently, characterization results implied that HZ-3 with the Si/Al ratio of 80 had the biggest mesoporous volume of 0.5193 cm3·g-1 on the basis of micropore volume around 0.1236 cm3·g-1, which was beneficial to the diffusion of reactant molecule; Raman spectra implied that there is a strong interaction between Ce and Ru. H2-TPR and O2-TPD showed that 5Ce0.5Ru/HZ-3 possessed the biggest consumption of hydrogen (0.486 mmol·g-1), surface adsorbed oxygen (0.683 mmol·g-1) and surface lattice oxygen (0.626 mmol·g-1), which was conducive to the adsorption and dissociation of reactant molecule; XPS showed 5Ce0.5Ru/HZ-3 had the biggest molar percentage of Ru4+ species (79.50%) and Ce3+ species (44.14%), which can induce the generation of much more oxygen vacancies. Overall, the introduction of Ce can result in the improvement of physical-chemical properties of 5Ce0.5Ru/HZ-3. Finally, the possible reaction route was given based on the in-situ DRIFTS and TD/GC-MS result.