The limited availability of noble metals spurred a quest for non-noble metal replacements. Here we will investigate the use of carbon supported Mo-carbides and W-carbides for the deoxygenation of vegetable oil/fat based feedstocks. Stability is a key issue for catalysis. Therefore we looked into that aspect in more detail. To that end the performance of both molybdenum- and tungsten carbide catalysts, supported on carbon(nanofibers) with large particles (10-12 nm) and small (2-4 nm) particles was investigated. The decarboxylation of stearic acid, via decarboxylation/decarbonylation/hydrodeoxygenation was used as case. The catalyst with the larger particles was more active compared to the one with the smaller particles. Moreover for W2C/CNF catalysts with small particles (2-4 nm) the selectivity to stearyl-stearate and octadecene at intermediate conversion levels was high, while at the catalysts with the larger particles a build-up of C18-oxygenates octadecanol and octadecanal was observed. This can be explained by a decrease in the amount of acidic ‘WOx’ domains on the catalyst with small particles, i.e. that catalyst is more easily oxidized. Upto now most of these reactions are performed in organic solvents. The stability of carbides in aqueous conditions is under dispute and therefore we investigated the stability of carbon nanofiber supported Mo-carbides and W-carbides in different solvents. Though the stability of the carbides in water is limited the stability does depend on the exact nature of the carbide phase. For example, WC is more stable in aqueous conditions compared to W2C. On the other hand in ethanol the stability of all phases is greatly enhanced. Therefore, these carbides still hold potential in replacing noble metal based catalysts in biomass conversion.

On the stability of supported carbides (Mo,W) for deoxygenation reactions

256th National Meeting (2018)

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