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

Abstract

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 O2 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 °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 °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.

Catalytic conversion of methane into benzene over ceria–zirconia‐promoted molybdenum‐supported zeolite for methane dehydroaromatization

“…It was assumed that the broad peak at 150°C was due to the adsorbed surface oxygen species reduced in this case. [ 58 ] In region I, CZO‐Mo/HZSM‐5 catalyst exhibited a strong and intense reduction feature which might be related to the mixing of two peaks: one corresponding to the reduction of polymeric molybdate moieties over the zeolite surface and the second peak was hypothesized due to the reduction of the small amount of Ce 4+ to Ce 3+ which are particularly active species in CZO surface. [ 32,58,59 ] Further, for the CZO‐impregnated Mo/HZSM‐5 catalyst, it was noted that the peak for the reduction of in region II shifted to a higher temperature with respect to conventional Mo‐doped HZSM‐5, which in turn suggests that the combination of CZO with Mo/HZSM‐5 might lead to the strong interaction of Mo‐oxo species with the surface, thus enhancing the reducibility of Mo oxide species bound to the surface.…”

“…[ 58 ] In region I, CZO‐Mo/HZSM‐5 catalyst exhibited a strong and intense reduction feature which might be related to the mixing of two peaks: one corresponding to the reduction of polymeric molybdate moieties over the zeolite surface and the second peak was hypothesized due to the reduction of the small amount of Ce 4+ to Ce 3+ which are particularly active species in CZO surface. [ 32,58,59 ] Further, for the CZO‐impregnated Mo/HZSM‐5 catalyst, it was noted that the peak for the reduction of in region II shifted to a higher temperature with respect to conventional Mo‐doped HZSM‐5, which in turn suggests that the combination of CZO with Mo/HZSM‐5 might lead to the strong interaction of Mo‐oxo species with the surface, thus enhancing the reducibility of Mo oxide species bound to the surface. [ 10,36 ] Further, in Figure 6b, CZO‐promoted Mo/HZSM‐5 revealed a very small hump or reduction feature in region III corresponding to the ( which indicates that as compared with the conventional Mo‐doped HZSM‐5 catalyst (which showed the large reduction feature), the probability of Mo oxide species undergoing in metallic Mo state was comparatively reduced.…”

“…It was assumed that the broad peak at 150 C was due to the adsorbed surface oxygen species reduced in this case. [58] In region I, CZO-Mo/HZSM-5 catalyst exhibited a strong and intense reduction feature which might be related to the mixing of two peaks: one corresponding to the reduction of polymeric molybdate moieties over the zeolite surface and the second peak was hypothesized due to the reduction of the small amount of Ce 4+ to Ce 3+ which are particularly active species in CZO surface. [32,58,59] Further, for the CZO-impregnated Mo/HZSM-5 catalyst, it was noted that the peak for the reduction of Mo 6þ !…”

Recent trends in phenol synthesis by photocatalytic oxidation of benzene

“…1b). [7][8][9][10][11][12][13] Most reported catalytic systems require harsh reaction conditions, such as high temperatures and pressures. Photocatalytic processes have attracted attention as "green" alternatives because they can activate benzene molecules using light as an energy source and convert them to phenol under mild reaction conditions.…”

Synthesis of NiGa2O4 ultra-thin nanosheets for improved xylene sensing properties and selectivity

“…[54][55][56] It is believed that this can be attributed to the strong Lewis acidity of Ni(II), which facilitates interaction with the pelectron cloud of benzene series. 57,58 Moreover, the density of the p-electron cloud in benzene is influenced by the nature and number of side chain groups. 59 Methyl groups are effective electron donors, meaning that the presence of more methyl groups will lead to a higher p-electron cloud density, thus increasing the reactivity towards benzene derivatives such as xylene.…”