Sustainable production of acrolein: effects of reaction variables, modifiers doping and ZrO2 origin on the performance of WO3/ZrO2 catalyst for the gas-phase dehydration of glycerol

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 H-2 or O-2); (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 degrees 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 O-2 to the reaction feed significantly reduced the catalyst deactivation rate but the AC selectivity was only slightly lowered. However, an addition of 4 kPa H-2 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 O-2-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%.