Abstract
Achieving high degree of active metal dispersions at the highest possible metal loading and high reducibility of the metal remains a challenge in Fischer Tropsch synthesis (FTS) as well as in hydrogeoxygenation (HDO).This study therefore reports the influence of oxalic acid (OxA) functionalization on the metal dispersion, reducibility and activity of Co supported ZSM-5 catalyst in FTS and HDO of oleic acid into paraffin biofuel. The Brunauer–Emmett–Teller (BET) results showed that cobalt oxalate supported ZSM-5 catalyst (CoOx/ZSM-5) synthesized from the incorporation of freshly prepared cobalt oxalate complex into ZSM-5 displayed increase in surface area, pore volume and average pore size while the nonfunctionalized cobalt supported on ZSM-5 (Co/ZSM-5) catalyst showed reduction in those properties. Furthermore, both XRD and XPS confirmed the presence of Co° formed from the decomposition of CoOx during calcination of CoOx/ZSM-5 under inert atmosphere. The HRTEM showed that Co species average particle sizes were smaller in CoOx/ZSM-5 than in Co/ZSM-5, and in addition, CoOx/ZSM-5 shows a clear higher degree of active metal dispersion. The FTS result showed that at CO conversion over Co/ZSM-5 and CoOx/ZSM-5 catalysts were 74.28% and 94.23% and their selectivity to C5+ HC production were 63.15% and 75.4%, respectively at 4 h TOS. The HDO result also showed that the CoOx/ZSM-5 has higher OA conversion of 92% compared to 59% over Co/ZSM-5. In addition CoOx/ZSM-5 showed higher HDO and isomerization activities compared to Co/ZSM-5.
Highlights
The depletion of fossil fuel reserves coupled with the attendant environmental pollution from its combustion as well as the recent fall in the crude oil prices globally have generated intensified research into alternative source of energy especially for the transport sector[1, 2]
Calcination temperature has a critical influence on the texture and crystallite size of supported catalyst based to the thermal response of the active metal precursors such as Co3O4 and hydrated cobalt (II) oxalate precursor (CoOx) (CoC2O4·2H2O) which in turn will affect the activity of the synthesized catalysts
CoOx/ZSM-5 showed two regions with increased weight loss within the first weight loss regions (WLR) and maximized at 154 °C according to Fig. 1b with a cumulative weight loss of 9.2% which can be ascribed to combined effect of the interlayer/physisorbed water molecules, hydration effect at the catalyst synthesis stage and complete dehydration of incorporated CoOx precursor (CoC2O4·2H2O) as shown in equation (2)
Summary
The depletion of fossil fuel reserves coupled with the attendant environmental pollution from its combustion as well as the recent fall in the crude oil prices globally have generated intensified research into alternative source of energy especially for the transport sector[1, 2]. Another study[16] compares the conversion of guaiacol and product yields over Al-MCM-41 supported Ni, Co, and Ni–Co catalysts at the same experimental conditions and 10Co/ Al-MCM-41 exhibited the highest HDO activity with least tendency towards gas phase yields for CH4, CO and CO2 In these studies, the challenges to catalyst designs and activities in upgrading fatty acids/biooil to transportation hydrocarbon fuels are similar to what were reported for the FTS which are active metal dispersion, active metal reducibility and proper MSI. The challenges to catalyst designs and activities in upgrading fatty acids/biooil to transportation hydrocarbon fuels are similar to what were reported for the FTS which are active metal dispersion, active metal reducibility and proper MSI To solve this problem, different studies such as effects of support, promoters, cobalt precursor and synthesis conditions have been explored[11, 13, 14, 17, 18]. The reducibility and other characterization results and activity of the synthesized catalyst were compared with another Co-supported ZSM-5 catalyst without OxA functionalization
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