Support effects and design rules for enhanced phosphotungstic acid catalyzed olefin oligomerization to sustainable aviation fuels

Abstract

Reducing the environmental footprint of aviation fuels requires catalysts that convert renewable olefins to jet-fuel hydrocarbons (JF). In this context, supported phosphotungstic acid (PTA) emerged as a promising Brønsted acid catalyst for this transformation. The performance of this catalyst depends strongly on the interaction of the PTA phase with the support. This study systematically investigates the interfacial electronic structure and surface functional chemistry of the support on oligomerization performance. 10 wt% PTA on oxide carriers (SiO 2 , ZrO 2 , Al 2 O 3 , and CeO 2 ) and on six functionalized activated carbons were prepared and examined by XRD, Raman, 31 P and 27 Al MAS NMR, XPS, and evaluated in propylene oligomerization. The oxide-supported catalysts separate into two behaviors with SiO 2 and ZrO 2 preserving the Keggin PTA, inducing moderate W-Si band bending, yielding extended acidic domains, and exhibiting superior propylene conversion with high selectivity to jet-fuel-range products (80%). In contrast, Al 2 O 3 and CeO 2 promote charge transfer, decomposing PTA into mixed inactive WO x /P–O species. Carbon supports allow decoupling of intrinsic metal-oxide redox properties from surface PTA-anchoring and polarity. The different functional groups influence the anchoring of the PTA units on the surface, from restructured non-Keggin PTA species to large or finely dispersed Keggin domains. Catalytic performance is enhanced when acidic (–COOH/phenol) and non-acidic/basic (ethers/carbonyls/amine) functional groups co-exist, creating sufficient though non-destructive electronic coupling and effective proton transfer. These findings provide design rules for supported PTA catalysts that emphasize support-mediated control over Keggin integrity, electronic coupling strength, and proton-transfer efficiency, irrespective of whether the support is an oxide or a functionalized carbon.