Synthesis and Characterization of Catalysts for the Selective Transformation of Biomass-Derived Materials

The experimental work in this thesis focuses on generating catalysts for two intermediate processes related to the thermal conversion of lignocellulosic biomass: the synthesis and characterization of mesoporous silica supported cobalt catalysts for the Fischer-Tropsch reaction, and an exploration of the reactivity of bulk and supported molybdenum-based nitride catalysts for the hydrodeoxygenation (HDO) of guaiacol, a lignin model compound. The first section of the work details the synthesis of a series of silicasupported cobalt Fischer-Tropsch catalysts with pore diameters ranging from 2-23 nm. Detailed X-ray diffraction measurements were used to determine the composition and particle diameters of the metal fraction, analyzed as a three-phase system containing Cofcc, Cohcp and CoO particles. Catalyst properties were determined at three stages in catalyst history: (1) after the initial calcination step to thermally decompose the catalyst precursor into Co3O4, (2) after the hydrogen reduction step to activate the catalyst to Co and (3) after the FT reaction. From the study, it was observed that larger pore diameters supported higher turnover frequency; smaller pore diameters yielded larger mole fraction of CoO; XRD on postreduction and post-FTS catalyst samples indicated significant changes in dispersivity after reduction. In the next section, the catalytic behaviors of unsupported, activated carbon-, alumina-, and SBA-15 mesoporous silica-supported molybdenum nitride catalysts were evaluated for the hydrodeoxygenation of guaiacol (2-methoxy phenol) at 300 oC and 5 MPa. The nitride catalysts were prepared by thermal decomposition of bulk and supported ammonium heptamolybdate to form MoO3 followed by nitridation in either flowing ammonia or a nitrogen/hydrogen mixture. The catalytic properties were strongly affected by the nitriding and purging treatment as well as the physical and chemical properties of support. The overall reaction was influenced by the crystalline phase present in the catalyst, dispersion of molybdenum nitride/oxynitride, and the porosity of the support. The hydrodeoxygenation of guaiacol followed two proposed reaction pathways: demethylation (DME) of guaiacol to form catechol, followed by dehydroxylation to form phenol; or a direct demethoxylation (DMO) to form phenol. The selectivity of the reaction was expressed in terms of the phenol/catechol ratio. Phenol was the predominant product for all the catalysts studied, except for the alumina-supported catalysts (an effect of the alumina support). The results from this thesis are encouraging for the application of Mo nitride based catalysts for hydrodeoxygenation of whole pyrolysis oil

Energy Production, Decontamination, and Hydrogenation Reactions over Perovskite-Type Oxide Catalyst

Heterogeneous catalysis is an important tool in industrial processes because of the recoverability of the catalysts. Transition metal perovskites-type oxides, with the general formula ABO3, offer attractive alternative to noble metal catalysts due to their high activity, high thermal stability, and low cost. Moreover, their physicochemical properties can be tailored to create a family of catalysts by varying the compositions of A and B. Indeed, the partial substitution at the A- and/or B-site with another metal cation stabilizes unusual oxidation states of the B cation with the simultaneous formation of structural defects. In particular, lanthanum-based perovskites have been used extensively and can be grouped into: (i) perovskites with oxygen vacancies as catalysts for oxidation reactions and (ii) perovskites as precursors to prepare nanosized catalysts for hydrogenation reactions. This chapter focuses on the use of pure and doped lanthanum perovskites as active and selective heterogeneous catalysts for catalytic energy production reaction (DME combustion), decontamination reactions (methane, acetyl acetate, toluene, n-hexane, and soot combustion), and hydrogenation reactions (guaiacol, glycerol, and xylose hydrogenation)

Methane selective oxidation on metal oxide catalysts at low temperatures with O₂ using an NO/NO₂ oxygen atom shuttle

Methane oxidation using O2 over transition metal oxides often requires severe conditions ( >500 °C) to achieve detectable conversion. In this study, NO was used to transfer oxygen atoms from O2, through the facile gas-phase formation of NO2 at moderate conditions (0.1 MPa and 300–400 °C), to oxidize methane over silica-supported transition metal oxides (VOx, CrOx, MnOx, NbOx, MoOx, and WOx). In situ infrared spectroscopy measurements indicated that the reaction likely proceeded by the formation of surface monodentate nitrate intermediates. These nitrate species were formed by the interaction between adsorbed NO2 and the supported metal oxides. During the reaction, the oxides of vanadium, molybdenum, and tungsten formed formaldehyde and CO2, whereas the oxides of chromium, manganese, and niobium produced only CO2. These results are consistent with the known hydrocarbon oxidation chemistry of the metal oxides. Contact time measurements on VOx/SiO2 indicated that formaldehyde was a primary product and CO2 was the final product; conversely, analogous measurements on MnOx/SiO2 showed that CO2 was the sole product. The formaldehyde production rate on VOx/SiO2, MoOx/SiO2, and WOx/SiO2, based on surface sites measured by high temperature oxygen chemisorption, compared favorably to oxygenate production rates for stronger oxidants (N2O and H2O2) reported in the literature

A review of advanced catalyst development for Fischer-Tropsch synthesis of hydrocarbons from biomass derived syn-gas

Fischer-Tropsch synthesis (FTS) is a process which converts syn-gas (H2 and CO) to synthetic liquid fuels and valuable chemicals. Thermal gasification of biomass represents a convenient route to produce syn-gas from intractable materials particularly those derived from waste that are not cost effective to process for use in biocatalytic or other milder catalytic processes. The development of novel catalysts with high activity and selectivity is desirable as it leads to improved quality and value of FTS products. This review paper summarises recent developments in FT-catalyst design with regards to optimising catalyst activity and selectivity towards synthetic fuels

Transition metal (Ti, Mo, Nb, W) nitride catalysts for lignin depolymerisation

Metal nitrides are promising catalysts for depolymerisation of lignin in supercritical ethanol; cheap and abundant titanium nitride affords an aromatic monomer yield of 19 wt% from soda lignin. The reaction mechanism is discussed on the basis of the products and a guaiacol model compound study

Catalytic Upgrading of Biomass Model Compounds: Novel Approaches and Lessons Learnt from Traditional Hydrodeoxygenation – a Review

Catalytic hydrodeoxygenation (HDO) is a fundamental process for bio‐resources upgrading to produce transportation fuels or added value chemicals. The bottleneck of this technology to be implemented at commercial scale is its dependence on high pressure hydrogen, an expensive resource which utilization also poses safety concerns. In this scenario, the development of hydrogen‐free alternatives to facilitate oxygen removal in biomass derived compounds is a major challenge for catalysis science but at the same time it could revolutionize biomass processing technologies. In this review we have analysed several novel approaches, including catalytic transfer hydrogenation (CTH), combined reforming and hydrodeoxygenation, metal hydrolysis and subsequent hydrodeoxygenation along with non‐thermal plasma (NTP) to avoid the supply of external H2. The knowledge accumulated from traditional HDO sets the grounds for catalysts and processes development among the hydrogen alternatives. In this sense, mechanistic aspects for HDO and the proposed alternatives are carefully analysed in this work. Biomass model compounds are selected aiming to provide an in‐depth description of the different processes and stablish solid correlations catalysts composition‐catalytic performance which can be further extrapolated to more complex biomass feedstocks. Moreover, the current challenges and research trends of novel hydrodeoxygenation strategies are also presented aiming to spark inspiration among the broad community of scientists working towards a low carbon society where bio‐resources will play a major role.Financial support for this work was provided by the Department of Chemical and Process Engineering of the University of Surrey and the EPSRC grants EP/J020184/2 and EP/R512904/1 as well as the Royal Society Research Grant RSGR1180353. Authors would also like to acknowledge the Ministerio de Economía, Industriay Competitividad of Spain (Project MAT2013‐45008‐P) and the Chinese Scholarship Council (CSC). LPP also thanks Comunitat Valenciana for her postdoctoral fellow (APOSTD2017)

A Comparative Cognitive Study of Happiness and Sadness Metaphors in Fante and English

The advent of cognitive linguistics has resulted in a change in the way people previously perceived metaphor as purely a linguistic device. Metaphor is now studied as a cognitive instrument that shapes our language, thought and action (Lakoff & Johnson, 1980; Kovecses, 2002). Native speakers of a language employ metaphors to express abstract concepts of emotions. This paper does a study of the happiness and sadness metaphors in English and Fante, a dialect of the Akan language spoken in Ghana. It is underpinned by Lakoff and Johnsons’ (1980) Conceptual Metaphor Theory which is adopted as the framework for analysis. The study found that the two languages share some similarities with regard to the use of conceptual metaphors such as happiness is a fluid in a container, happiness is being off the ground, sadness is a fluid in a container and sadness is an object. The differences in the use of these conceptual metaphors are very minimal and can be ascribed to the different cultural practices that are prevalent in the two languages. The study recommends that teachers of language integrate metaphor awareness into their curriculum to help learners have a better understanding of metaphorical expressions to improve their communication skills. Additionally, there should be an expansion of studies on conceptual metaphors to cover more Ghanaian and African languages to enrich cognitive linguistic theory

Bald On-Record Politeness Strategy in Parliamentary Debates of the Parliament of Ghana

This paper examines how face needs are seemingly disregarded in parliamentary discourse, and the circumstances that frame such apparent infractions. Pivoting around politeness theory, politeness principles and maxims of conversation, the study uncovers means and ways in which Members of the Parliament of Ghana engage one another in debates on often contentious issues of national importance. By an analysis of content, the study identifies insults, accusations and imperatives as bald strategies used by the parliamentarians. All the actors in the debates – the Speaker, Majority MPs, Minority MPs – employed bald on-record utterances in a variety of ways and from either provocative or corrective positions in the discourse. The findings suggest that the Standing Orders on debates in the House are framed, in part, within the maxims of conversation proposed by Grice (1975), and they guide and influence the Members’ use of politeness strategies during the debates. Besides, Members tended to commit face-threatening acts when they correctively pointed out that a previous speaker had flouted the maxims of quality and relevance. In view of the findings, the study recommends that closer attention be given to the role of context in the research on politeness. Keywords: Politeness, Conversational Maxims, Context, Parliament, Standing Orders, Bald on-record DOI: 10.7176/JLLL/102-09 Publication date: July 30th 202