title: Novel catalytic materials for syngas related reactions
Creators: name: Irvine, Nicola
Publisher: name: University of Glasgow
Year: 2021
Subjects: subject: Syngas, catalysis, hydrogenation.

description: Synthesis gas (syngas) can be sourced from waste biomass via gasification generating a mixture of CO/H2 which can be catalytically converted into liquid chemicals. Production of liquid products in this manner is often referred to as Fischer-Tropsch (F-T) technology, which is becoming of increasing importance to generate these liquid chemicals in a sustainable way. F-T technology uses a catalyst to convert H2/CO into alkanes, alkenes or oxygenated products, and the catalyst used dictates the product produced. Common F-T catalysts comprise iron (Fe) or cobalt (Co) and it is important to highlight that nickel (Ni) has been utilised as a methanation catalyst. Fe-based catalysts are known to produce alkanes, alkenes and oxygenates (oxygen-containing species), whereas Co-based catalysts are known to produce alkanes. Nevertheless, separation of such products can add a large economic cost to the process which has led to continuation of catalyst development aimed at improving catalyst selectivity. Consequently, this project has looked at modifying Co, Fe and Ni-based catalysts (as each transition metal has previously shown CO hydrogenation activity) with boron (B) or phosphorus (P) to investigate the catalyst’s selectivity. A series of metal boron materials were synthesised via a sodium borohydride (NaBH4) reduction methodology with varied metal: B molar ratios. I.C.P. analyses confirmed the presence of B within each material and did not show any significant trend that could be related to the modified activity. B-modifications led to decreased activity compared to benchmark catalysts, however the Co-B and Co-B/SiO2 (1:1, Co:B) catalyst’s selectivity had been modified to produce C7-C15 alkenes alongside C7-C20 alkanes. Co-B/SiO2 (1:3) material was modified in such a manner to selectively produce light C1-C3 hydrocarbons only. Fe-B/SiO2 (1:5) produced light C1-C3 hydrocarbons only and the Fe-B material selectively produced C10-C20 alkanes. Modified Ni catalysts showed a decrease in methanation activity however showed increased water gas shift (WGS) activity. A combination of characterisation techniques has suggested different metal environments and XAS results have shown the occurrence of different transition metal oxidation states. It may be possible that the B modifications have altered the electronic structure of each metal in such a manner that hindered CO adsorption thus leading to lower catalytic activity. XPS results also showed additional surface species such as BOx, Na and Cl were present in some materials that may have hindered H2 and CO adsorption thus leading to lower catalytic activity. An additional series of transition metal phosphides were prepared and tested, where each Fe-based material showed significantly reduced activity, only producing trace amounts of C1-C3 products. However, bulk Co2P had been modified in such a manner to produce alkanes, alkenes and oxygenated products. Ni2P also showed interesting activity and produced C10-C20 alkanes. XAS results suggested that the Co system had undergone a structural rearrangement which may have resulted in deactivation whereas the Ni system did not appear to be altered. Raman analysis suggested subtle electronic structural differences between the supported and bulk systems that may have contributed to the results however further in-situ characterisation would be required to expand upon this theory.