Generation and use of nanoparticles for selective organic transformation

Alsharif, Heba 2023. Generation and use of nanoparticles for selective organic transformation. PhD Thesis, Cardiff University. Item availability restricted.

Preview	PDF - Accepted Post-Print Version Download (8MB) | Preview
	PDF (Cardiff University Electronic Publication Form) - Supplemental Material Restricted to Repository staff only Download (575kB)

Abstract

Environmental pollution and global warming have become significant challenges for modern-day society because of our reliance on non-renewable resources. One of the obvious choices for renewable resources is plant biomass. Furfural and 5- hydroxymethylfurfural, which are platform chemicals derived from plant biomass, have become essential components in various chemical transformations and applications. It is remarkable how these building blocks can be used in many ways to achieve desired outcomes. Their source, versatility, and efficacy make them a popular choice among researchers and industries alike. The reactivity observed in Furfural and 5- hydroxymethylfurfural is attributed to the presence of various functionalities, including C=O, C=C, and C-O bonds. Hence, one of the objectives of this thesis is to design and synthesise new heterogeneous catalysts for the chemoselective hydrogenation of biomass-derived, furan-based, platform molecules. Furthermore, selective cleavage of the C-O bond to open the furan ring in 5-hydroxymethylfurfural in the presence of other functional groups is another objective we set out to achieve in this thesis. In this study, the hydrogenation of furfural to furfuryl alcohol with high selectivity has been accomplished by using supported catalysts with enhanced active sites achieved via different post-synthesis thermal treatment protocols. The post-synthesis heat treatment protocols employed are calcination only (Calc), reduction only (Red) and calcination and reduction (Calc + Red). Interestingly, 97% conversion of furfural with 95% selectivity to 2-FFA was achieved on 0.6% Pt/TiO2 with Calc + Red post-synthesis thermal treatment. The first stage of this research screened the effect of different supports on the hydrogenation of furfural. Monometallic platinum nanoparticles (Pt-NPs) supported on different supports (TiO2, Nb2O5, CeO2, SiO2 and C) were synthesised using the wet impregnation method and were later subjected to various post-synthesis heat treatment protocols. Catalysts screening were carried out at 30 °C under hydrogen (3-bar) in a Colaver glass reactor for 1-6 h. Pt/TiO2 is the most promising catalyst with highest conversion and selectivity for furfuryl alcohol. Different Pt loadings were tested, and 0.6% Pt/TiO2 (with Calc + Red post-synthesis thermal treatment) catalyst is the best with 97% conversion and 95% selectivity for furfuryl alcohol. We postulated that the catalyst’s V activity and selectivity is due to the active site not being covered by the support material (TiO2). Detailed characterisation using XPS, TEM, and CO chemisorption techniques reveals the presence of nano-sized and highly distributed Pt0 species on the surface of the catalyst. The formation of Pt0 species, responsible for the high activity and selectivity observed, is influenced by post-synthesis heat treatment protocols. The Pt0 species improved selectivity to furfuryl alcohol by adsorbing the carbonyl group of furfural preferentially, rather than the alkene group on the surface of the catalyst. Chapter 4 describes the liquid phase hydrogenation of furfural over monometallic catalysts (Au, Ru, Pd) and bimetallic nanoparticles (RuPt, RuPd, AuPt and PtPd) supported on TiO2 and the results obtained are compared to that of monometallic platinum catalyst (0.6% Pt/TiO2 Calc + Red). Pt/TiO2 catalyst with Calc + Red post-synthesis heat treatment was used as a reference in this work owing to its high activity and selectivity in the hydrogenation of furfural. In order to improve the catalytic hydrogenation of furfural activity, these monometallic and bimetallic catalysts have been explored as alternative metals to platinum. These catalysts have been prepared by the method described in chapter 2 and characterised by XPS, TEM and CO chemisorption. The hydrogenation of furfural over these catalysts exhibited different catalyst activity and product distributions. The results obtained show that bimetallic PtRu/TiO2 catalyst with Calc + Red post-synthesis heat treatment is the best out of all the catalysts screened. However, the PtRu/TiO2 Calc + Red catalyst presented poor stability and recyclability, with loss of activity after three cycles. Sintering of the NPs during the hydrogenation of FF was identified as the main reason for catalyst deactivation. In addition, the effect of the second metal on the catalyst’s activity, selectivity and stability relative to Pt/TiO2 Calc + Red was explored. In chapter 5, direct transformation of 5-hydroxymethylfurfural to 1,6-hexanediol by a monometallic Pt-NPs and a series of bimetallic catalysts (PtPd, PtCo, PtRu and PtRe) on different support was investigated. The catalysts were prepared by wet impregnation method after which they were reduced in the furnace for 4 h at 450°C with 5 vol.% H2/Ar. 5wt% PtRu/HAP catalyst exhibits the best activity in the direct conversion of 5- hydroxymethylfurfural to 1,6-hexanediol via hydrogenation/hydrogenolysis. The catalyst selectivity towards 1,6-hexanediol is found to be a function of the acid-base properties of VI the hydroxyapatite support which is in line with what has been reported in literature. The effect of different reaction conditions was investigated by using different polar protic solvents, varying the temperature, H2 pressure and reaction time. PtRu/HAP catalyst presented high stability after three cycles without loss of activity and the synergistic effect between the PtRu nanoparticles (NPs) and the acid-base properties of the hydroxyapatite support play a key in the catalyst activity and selectivity towards 1,6-HDO. The overall conclusion of the thesis: the strong metal support interaction between Pt and reducible support (TiO2) is significantly affected by the heat treatment protocol as effective for the formation of Pt0 on the catalyst surface, which is crucial for the selective hydrogenation of the carbonyl group in furfural to furfuryl alcohol under mild reaction conditions (30 °C, 3 bar of H2 using Pt/TiO2 cal + red catalyst). Also, this thesis has exhibited that the bimetallic catalyst PtRu/HAP is a more effective catalyst for the ring opening of HMF under mild reaction conditions compared to analogues monometallic catalysts.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Date of First Compliant Deposit:	1 March 2024
Last Modified:	01 Mar 2025 02:30
URI:	https://orca.cardiff.ac.uk/id/eprint/166757

Actions (repository staff only)

Edit Item