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The effect of chloride ions on a monoclinic ZrO_2-supported RuO_x(RuO_x/m-ZrO_2) catalyst with a Ru surface density of 0.3 Ru/nm~2 was studied in the selective oxidation of methanol to methyl formate(MF) at a low temperature of 373 K.The m-ZrO_2 support was Cl-free,and Cl~- ions were introduced into the RuO_x/m-ZrO_2 catalyst by impregnation with zirconium oxychloride or ammonium chloride and subsequent thermal treatment in air at 673 K.The structures of these catalysts were characterized by X-ray diffraction,Raman and X-ray photoelectron spectroscopies.Their reducibility was probed by temperature-programmed reduction in H_2.The RuO_x domains were present as highly dispersed RuO_4~(2-) structure on m-ZrO_2 with similar reducibility for the RuO_x/m-ZrO_2 samples irrespective of modification with or without Cl~- ions.Introduction of appropriate amounts of zirconium oxychloride into RuO_x/m-ZrO_2 led to a remarkable increase in the methanol oxidation rate and MF selectivity,whereas introduction of ammonium chloride or zirconyl nitrate significantly inhibited the catalytic performance of RuO_x/m-ZrO_2.The promoting effect of Cl~- ions derived from zirconium oxychloride can be tentatively attributed to their roles in facilitating the adsorption of methanol and desorption of MF product or its intermediates.This finding provides novel insights into the promoting effect of Cl~ ions on oxides-based catalysts for selective oxidation reactions.
The effect of chloride ions on a monoclinic ZrO 2 -supported RuO_x (RuO_x / m-ZrO_2) catalyst with a Ru surface density of 0.3 Ru / nm ~ 2 was studied in the selective oxidation of methanol to methyl formate (MF) at a low temperature of 373 K. The m-ZrO 2 support was Cl-free, and Cl ~ - ions were introduced into the RuO x / m-ZrO 2 catalyst by impregnation with zirconium oxychloride or ammonium chloride and subsequent thermal treatment in air at 673 K. The structures of these catalysts were characterized by X-ray diffraction, Raman and X-ray photoelectron spectroscopies. Their reducibility was probed by temperature-programmed reduction in H_2. The RuO_x domains were present as highly dispersed RuO_4 ~ (2-) structure on m-ZrO_2 with similar reducibility for the RuO_x / m-ZrO_2 samples irrespective of modification with or without Cl ~ - ions. Introduction of appropriate amounts of zirconium oxychloride into RuO_x / m-ZrO_2 led to a remarkable increase in the methanol oxidation rate and MF selectivity, in introd uction of ammonium chloride or zirconyl nitrate significantly inhibited the catalytic performance of RuO_x / m-ZrO_2. The promoting effect of Cl ~ - ions derived from zirconium oxychloride can be tentatively attributed to their roles in facilitating the adsorption of methanol and desorption of MF product or its intermediates. This novel provides insights into the promoting effect of Cl ~ ions on oxides-based catalysts for selective oxidation reactions.