Tandem hydrogenation-esterification of furfural using bifunctional metal-supported nanoparticle catalysts / Muhammad Luqman Hakim Hashim

Muhammad Luqman Hakim , Hashim (2023) Tandem hydrogenation-esterification of furfural using bifunctional metal-supported nanoparticle catalysts / Muhammad Luqman Hakim Hashim. PhD thesis, Universiti Malaya.

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Abstract

The exploration of renewable resources such as rice husk for energy application is important against the fossil counterparts. Developing one-pot reaction methodologies is crucial for sustainable production of bio-derived fuels and chemicals, which typically requires a multifunctional catalyst system. This thesis reported on the one-pot process hydrogenation-esterification of furfural to furfuryl acetate using a bifunctional metal-based nanostructured catalyst, composed of rice husk (RH) derived SiO2, Cu, Al, and Mg species (RHSiO2-Cu-Al-Mg). Al and Mg metals were introduced to form RHSiO2-Cu-Al and RHSiO2-Cu-Al-Mg respectively to further improve the catalyst’s reusability and performance. The catalyst’s surface area was improved with the latter catalyst having a specific surface area of 150 m2/g. The catalytic efficiency of RHSiO2-Cu and RHSiO2-Cu-Al were also tested against RHSiO2-Cu-Al-Mg as points of comparison. Various analytical techniques were used to elucidate the physicochemical, textural, and acid-redox properties of the catalysts. It was found that the RHSiO2-Cu-Al-Mg catalyst contains an optimum amount of acid and redox sites, as demonstrated in the NH3-TPD and H2-TPR studies. Mg addition played a pivotal part in tuning the acidity of the RHSiO2-Cu-Al catalyst to promote the in-situ esterification of furfuryl alcohol with acetic acid to yield furfuryl acetate. As a result, the RHSiO2-Cu-Al-Mg catalyst exhibited the best performance in one-pot hydrogenation-esterification of furfural to furfuryl acetate (24.5% selectivity), outperforming various noble metal/silica-based catalysts. Following these results, single-atom catalysts (SACs) were developed from three metals; Pd, Ni, and Cu and their lattice strain influence on tandem hydrogenation-esterification of furfural were carefully monitored. It was observed that a low level of lattice strain in SACs tend to induce high and selective conversion of furfural to furfuryl acetate. SACs with high lattice strains have low chemical transformation performance due to poor reorientation of the active site that minimized the H2 coverage. These results validated that despite some SACs having > 95 % crystal structure perfection, small difference (< 0.1 %) in the lattice strain may induce SACs' relatively poor performance. Lastly this study focused on surface structures of nanoparticle catalysts which are mainly controlled by the hydrogen potential (pH) which are central to the promotion of selective catalysis for the production of fuels and chemicals-based substances that find domestic and industrial relevance. In this study, four different pH domains; 1, 3, 7 and 10 were employed to synthesis RHSiO2-Cu-Al-Mg nanoparticle catalyst using the one-pot procedure. It was observed that the acidic domain (pH 1and 3) provided high lattice strain (0.425 % and 0.322 %) while the basic domain (10) provided low lattice strain (0.160 %). The lattice strain (0.127 %) at neutral pH (7) was less than that of the acidic but greater than basic domain. The activity of RHS iO2-Cu-Al-Mg nanoparticle catalyst in terms pH of 1, 3, 7 and 10 are 95.8, 78.5, 95.1 and 94.3 selective to furfuryl alcohol respectively. Similarly at the same pH domain, the catalyst was 4.2, 21.5, 4.9 and 5.7 % selective to furfuryl acetate respectively during one step hydrogenation esterification reaction.

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