Catalytic behaviour of mesoporous metal phosphates in the gas-phase glycerol transformation

• Simple (M = Al, Fe, Co, Mn) and binary (Al/M; M = Fe,V,Ca) metal phosphates presented good stability.
• Acidity, redox sites and morphology of metal phosphates are influential in acrolein formation.
• Amorphous Fe and Al phosphates were more active than those with a high crystalline character (Co, Mn, Cu).
• Al-V phosphate composed of partially-crystallised AlPO4 and β-VOPO4, showed the highest activity in the acrolein formation

The catalytic behaviour of mesoporous simple (M = Al, Fe, Co, Mn) and binary (Al/M; M = Fe,V,Ca; molar ratio Al/Fe = 50; Al/V = 2; Al/Ca = 1) metal phosphates, synthesized by an economical gelation method, in the gas-phase glycerol reaction at temperatures between 220 °C and 280 °C, has been investigated. The morphology, textural properties and the acidity by pyridine TPD, of the phosphates were also determined. The activity of the phosphates in the formation of the main reaction product (acrolein) depended not only on their acidity (mainly acid sites of weak-medium strength) but also on the redox sites and morphology exhibited. Thus, the aluminium-vanadium phosphate showed the highest value of yield to acrolein, 62% (equivalent to a productivity of 0.88 gACRgcat⋅h) at 280 °C, whereas the amorphous FePO4 and AlPO4 were appreciably more active than the rest of the simple phosphates, exhibiting a high crystalline character. The apparent activation energy values obtained for the acrolein formation ranged between 18 and 91 kJ/mol. Based on the identified products in this study, some possible reactions involved in the glycerol transformation have been suggested.

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