Novel highly active Ag–SiO 2–Al 2O 3–ZnO catalyst for the production of anhydrous HCHO from direct dehydrogenation of CH 3OH

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A novel four-component Ag–SiO 2–Al 2O 3–ZnO catalyst prepared by sol–gel method shows an outstanding catalytic activity (99% conversion and 87% selectivity) during the process of the direct dehydrogenation of methanol to anhydrous formaldehyde (HCHO). The optimal preparation conditions were found to be 20 wt.% loading of silver and zinc content of 15%. The catalytic activity was measured in the temperature range 450–700 °C and at the space velocity of 1 × 10 4 h −1, while the optimum reaction temperature was determined to be 650 °C. The catalyst was characterized by several kinds of methods: BET method of nitrogen adsorption at −196 °C, TG–DTG, SEM, XRD, and NH 3-TPD. The catalysts were white powder-like materials and that the BET surface area was ∼0.5 m 2 g −1. All silver was present in an ionic state in the framework of the SiO 2–Al 2O 3–ZnO carrier before catalytic reaction and was thermally stable up to 1000 °C. After the reaction, silver was present in the crystalline metal state. The particles were smaller than those found on Ag–SiO 2–Al 2O 3 catalyst.