Insights into reaction mechanisms of catalytic hydrogen production from alcohols : a density functional theory study
MetadataShow full item record
Securing the world's clean energy future in the form of sustainable H₂ generation is a key challenge. Alcohols (and eventually carbohydrates from bio-waste) are potential carriers for H₂ storage, from which H₂ needs to be liberated catalytically. Morton and Cole-Hamilton have presented a classic catalytic system for dehydrogenation and decarbonylation of primary alcohols including methanol (Morton and Cole-Hamilton et al. 1988). A water gas shift reaction (WGSR) would allow the liberation of another equivalent of H₂. We now present a Density Functional Theory (DFT) investigation, using the B97-D dispersion-corrected functional, to probe the viability of such a pathway and to help design a system that can catalyse all processes, including dehydrogenation, decarbonylation and WGSR, equally well. Two different catalytic cycles that depart from those in molecular hydrogen production under basic conditions catalysed by [RuH₂(CO)(PPh₃)₃] (22) have been studied, the first involving a WGSR and the second covers the formation of gem-diol-(ate), formic acid and finally the CO₂ elimination. The overall computed energy barrier for the attack of water (in the form of OH⁻) on the CO ligand of complex 22 is prohibitively high because this attack is predicted to be highly endergonic; therefore, a WGSR is not plausible with this species. An alternative catalytic cycle for this process has been characterised computationally, starting from the formaldehyde complex (35) through the formation of a gem-diolate species, subsequently forming formic acid and, finally, CO₂. The gem-diolate pathway has insurmountable barriers, too. Another catalytic cycle involving complex [RuH₂(CO)₂(PPh₃)₂] (58) is characterised as a result of a second decarbonylation reaction where the attack of OH⁻ on the CO ligand is reasonable. Complete dehydrogenation of alcohols could thus be possible under basic conditions.
Thesis, MPhil Master of Philosophy
Embargo Date: 2021-02-15
Embargo Reason: Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 15th February 2021. Restriction now expired. Awaiting final permissions to release or further restrict full text.
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.