Enhanced coking-resistance of Ca- and Mg-incorporated Mo/V montmorillonite-supported catalysts during gas-phase glycerol conversion to allyl alcohol

Abstract

The efficient production of allyl alcohol from glycerol is of great importance due to its significance as a valuable intermediate in chemical industries. During the catalytic conversion of glycerol to allyl alcohol by solid acid catalysts, carbon deposition (coking) is prone to occur on the catalyst surface, leading to slowing of the conversion process and fast deactivation of the catalyst. In this study, we obtained an efficient catalyst for the preparation of allyl alcohol from gas-phase glycerol by controlling the pore structure and surface acidity of the catalyst. The characterization results showed that hydrochloric acid and citric acid removed the silicon and aluminium elements from montmorillonite. Additionally, the acidity, pore volume, and surface area ratio of Na-MMT (S_BET = 34.5 m² g⁻¹, V_T = 0.19 cm³ g⁻¹) were all found to be improved in porous montmorillonite (HA₁MMT) catalyst (S_BET = 97.9 m² g⁻¹, V_T = 0.28 cm³ g⁻¹). After adding MoO_x and VO_x, the selectivity of the Mo/V-HA₁MMT catalyst for allyl alcohol was improved. XPS characterization results indicate that the synergistic effect of Mo and V can promote the transfer of electrons during the reaction process of glycerol conversion. Within 480 min of catalyzing the glycerol dehydration reaction, Mo_0.6V_0.4(5)-HA₁MMT was almost deactivated (conv. = 19.5%, sel._{allyl alcohol} = 31.2%) due to carbon deposition. When the catalyst was doped with calcium and magnesium components, a new active phase CaMo₄ was discovered on the catalyst, and the acidity of Ca_0.5Mg_0.5-Cat. (Cat. is Mo_0.6V_0.4(5)-HA₁MMT) decreased to 214.0 μmol g⁻¹. The coking-resistance performance of Ca_0.5Mg_0.5-Cat. was improved, and after 660 min of reaction, the catalyst was deactivated (conv. = 32.1%, sel._{allyl alcohol} = 30.1%) due to carbon deposition. During the 3rd catalyst regeneration test, Ca_0.5Mg_0.5-Cat. still maintained high activity (conv.= 63.3%, sel._{allyl alcohol} = 35.2%, sel._acrolein = 31.2%). These results indicate that suitable pore structure and acidity are crucial for designing a catalyst with coking-resistance properties.