Sustainable production of acrolein: effects of reaction variables, modifiers doping and ZrO2origin on the performance of WO3/ZrO2catalyst for the gas-phase dehydration of glycerol

Abstract

Zirconia-supported tungsten oxide (WO3/ZrO2 or WZ) is known as an efficient catalyst for selective acrolein (AC) production from gas-phase dehydration of glycerol (GL). Two catalysts (WZ-CP and WZ-AN) were prepared herein using, respectively, a ZrO(OH)2 hydrogel (ZrO(OH)2-CP) and its derived alcogel (ZrO(OH)2-AN) for a precursor of ZrO2. To optimize the reaction variables and improve the catalyst performance, the WZ-CP catalyst was employed to show the effects of (A) reaction variables (temperature, partial pressures of GL and H2O, and co-feeding H2 or O2); (B) catalyst modification with alkali and alkali earth metal ions (Na+, K+ and Mg2+), or transition metals (Pt, Pd, Rh and Ni). The reaction at 315 °C always produced the highest AC selectivity, and this temperature was then used to investigate the effects of the other variables and catalyst modifications. Increasing the molar GL/H2O ratio led to lower AC selectivity and accelerated the catalyst deactivation. Introducing 4–8 kPa O2 to the reaction feed significantly reduced the catalyst deactivation rate but the AC selectivity was only slightly lowered. However, an addition of 4 kPa H2 produced almost no effect on the reaction. The modified catalysts performed no better during the reaction unless the modifier was Pt or Pd, whose catalytic stabilities in the O2-containing (4 kPa) feed were significantly higher and their selectivity for AC production slightly lowered. Working under the conditions optimized with WZ-CP, the WZ-AN catalyst offered a high AC yield (62–68%) for longer than 30 h, during which the GL conversion remained higher than 93%.