Preparation of earth abundant metal mesoporous silica materials with implications for the production of liquid fuels

Abstract

The global maritime fleet is an integral part of the United States economy, albeit at the cost of substantial contributions to atmospheric particulate matter, SOx, and NOx. This is further confounded by the inadequacies of electrification to provide clean alternative to conventional diesel engines. Fortunately, methanol fuels are poised to reduce emissions in commercial shipping, while Fischer-Tropsch synthesis of diesel can reduce dependence on foreign petroleum. Efforts can be improved by new facile routes towards SiO2 supported earth abundant metals such as Cu and Fe. Through HRTEM, RAMAN, FTIR, ICP-AES, N2 physisorption, HRTEM, EDAX, 57Fe Mössbauer spectroscopy, SAXS, and XRD we investigate the structure and composition of these mesoporous silica embedded earth abundant metal materials. In addition, where applicable we demonstrate the accessibility of metal sites. Cu functionalized zeolites show high activity for partial oxidation of methane to methanol. We developed a facile and reagent-free process for 3-5 nm Cu rich nanoparticles on commercial ZSM-5 carried out through electrolysis of Cu. The method was applied over various times, voltages, and supports. Beyond methanol, Fischer-Tropsch diesel depends on low cost Fe catalysts. Unfortunately, high temperature carburization routes used to convert Fe to Fe-carbides as well as operating conditions induce sintering of the metal particles, hindering catalysis. We have proposed a method to stabilize metals against sintering by substitution of Fe within the SiO2 framework. Strategies to incorporate Fe within mesoporous silica SBA-15 involve lowering the acidity of the synthesis gel which detrimentally effects the morphology of the final catalyst. Multi-step chemical routes may be used at the cost of complexity. Addition of the diammonium phosphate to the synthesis gel of SBA-15 improves Fe content from 0.04 to 10.14 wt. % with surface area of 613 m2 g-1. We also explored the feasibility of minimizing aqueous solvent in favor of imidazole ionic liquids. With the ability to self-assemble and dissolve metal salts 1-butyl-3-methylimidiazole tetrafluoroborate has been shown to be a suitable alternative to water as a solvent system to produce mesoporous silica embedded iron materials with surface areas near 600 m2g-1, 10 nm pores, 1.8 wt. % Fe content.