Abstract
Mesoporous CuO-ZrO2 catalysts were prepared and calcined at 500 °C. The performance of the synthesized catalysts for benzylation of benzene using benzyl chloride was studied. The bare support (macroporous ZrO2) offered 45% benzyl chloride conversion after reaction time of 10 h at 75 °C. Significant increase in benzyl chloride conversion (98%) was observed after CuO loading (10 wt. %) on porous ZrO2 support. The conversion was decreased to 80% with increase of CuO loading to 20 wt. %. Different characterization techniques (XRD, Raman, diffuse reflectance UV-vis, N2-physisorption, H2-TPR, XPS and acidity measurements) were used to evaluate physico-chemical properties of CuO-ZrO2 catalysts; the results showed that the surface and structural characteristics of the ZrO2 phase as well as the interaction between CuO-ZrO2 species depend strongly on the CuO content. The results also indicated that ZrO2 support was comprised of monoclinic and tetragonal phases with macropores. An increase of the volume of monoclinic ZrO2 phase was observed after impregnation of 10 wt. % of CuO; however, stabilization of tetragonal ZrO2 phase was noticed after loading of 20 wt. % CuO. The presence of low-angle XRD peaks indicates that mesoscopic order is preserved in the calcined CuO-ZrO2 catalysts. XRD reflections due to CuO phase were not observed in case of 10 wt. % CuO supported ZrO2 sample; in contrast, the presence of crystalline CuO phase was observed in 20 wt. % CuO supported ZrO2 sample. The mesoporous 10 wt. % CuO supported ZrO2 catalyst showed stable catalytic activity for several reaction cycles. The observed high catalytic activity of this catalyst could be attributed to the presence of a higher number of dispersed interactive CuO (Cu2+-O-Zr4+) species, easy reducibility, and greater degree of accessible surface Lewis acid sites.
Highlights
Zirconium oxide (ZrO2 ) has been used as a catalyst and support mainly because of its unique properties as it can possess relatively high surface area, the preservation of both acid and basic sites and possession of redox properties [1]
We studied the physico-chemical properties of synthesized porous CuO-ZrO2 catalysts to understand the nature of interaction between CuO and
It is known that X-ray diffraction (XRD) reflections appear at low angles due to regular separation between single channel walls [21]
Summary
Zirconium oxide (ZrO2 ) has been used as a catalyst and support mainly because of its unique properties as it can possess relatively high surface area, the preservation of both acid and basic sites and possession of redox properties [1]. It is mechanically and thermally stable; as a result, ZrO2 has been used as a structural promoter and, more frequently, as a support material in many catalytic applications. As part of our continued research, we synthesized ordered mesoporous CuO-ZrO2 catalysts and studied their structural properties to investigate the nature of interaction between CuO and ZrO2 and its role in benzylation of benzene. To the best our knowledge, no report exists on the synthesis of ordered mesoporous CuO-ZrO2 catalysts with high CuO content (10 and 20 wt. %) and their utilization for benzylation of benzene
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