Characterization of Surface Species during Benzene Hydroxylation over a NiO-Ceria-Zirconia Catalyst

NiO/ceria-zirconia (CZ) is a promising catalyst for the selective oxidation of benzene, as the Lewis-acidic NiO clusters can activate C-H bonds and the redox-active CZ support can activate O-2 and supply active oxygen species for the reaction. In this study, we used transmission in situ infrared (IR) spectroscopy to examine surface species formed from benzene, water, oxygen, phenol, and catechol on a NiO/CZ catalyst. The formation of surface species from benzene and phenol was compared at different temperatures in the range of 50-200 degrees C in the presence and absence of water vapor. We also examined the role of the NiO clusters and the CZ support during benzene activation by comparing the surface species formed on NiO-CZ with those formed on a Ni-free CZ support and on a NiO/SiO2 catalyst. The spectrum of surface species from dosing benzene at 180 degrees C provides evidence for C-H bond activation. Specifically, the observation of C-O stretching vibrations indicates the formation of phenolate species. Introduction of water enhances these IR signals and introduces several additional peaks, indicating that a variety of different surface species are formed. These results show that NiO/CZ could catalyze direct conversion of benzene to phenol.

Automated summary

NiO/ceria-zirconia (CZ) is a promising catalyst for the selective oxidation of benzene, with Lewis-acidic NiO clusters activating C-H bonds and the redox-active CZ support supplying active oxygen species for the reaction. In this study, surface species formed from benzene, water, oxygen, phenol, and catechol on a NiO/CZ catalyst were examined using transmission in situ infrared (IR) spectroscopy. The presence of NiO clusters and the CZ support played crucial roles in benzene activation, leading to the formation of different surface species and indicating the potential of NiO/CZ for catalyzing the direct conversion of benzene to phenol with the addition of water enhancing the reaction process.