Product inhibition in the glycerol oxidation over Au/TiO2 catalyst quantified by NMR relaxation

Liquid-phase catalytic oxidation of glycerol in aqueous solutions using porous solid catalysts represents a viable strategy for the sustainable production of fine chemicals from renewable resources. Various aspects of this novel type of reactions are still under investigation. Catalyst deactivation is one of those issues that need to be understood and addressed in order to make these processes commercially viable. In a previous study it has been reported that the catalytic activity of Au/TiO2 catalysts for the oxidation of glycerol with O2 under basic conditions can be severely inhibited by some reaction intermediates or products. It was suggested that the presence of certain species blocks the active sites of the catalyst, preventing the adsorption of glycerol, which in turn results in a decrease of reaction rate. In this work, we used NMR relaxation time measurements in order to assess surface interactions of glycerol in Au/TiO2 catalyst pre-treated with aqueous solutions of various oxygenates, including intermediates and products of glycerol oxidation, under basic conditions, in particular evaluating changes in glycerol adsorption properties. The NMR T1/T2 ratio of glycerol, which is indicative of the strength of interaction of glycerol with the catalyst surface, traces out well the trend in catalytic activity in the presence of different additives, suggesting that adsorption of glycerol onto the catalyst surface play a crucial role in the reaction, which supports the hypothesis previously made in the literature. This experimental approach and the related results represent a significant advance in the understanding of liquid-phase catalytic reactions occurring over solid surfaces, which can be used to understand and optimise catalytic processes and the effect of intermediate and product inhibition

Solvent inhibition in the liquid-phase catalytic oxidation of 1,4-butanediol: understanding the catalyst behaviour from NMR relaxation time measurements

Catalytic reaction studies and Nuclear Magnetic Resonance (NMR) relaxation time measurements have been compared to study the influence of competitive adsorption of reactant and solvent on catalytic conversion. The reaction chosen is the aerobic catalytic oxidation of 1,4-butanediol in methanol over different supported-metal catalysts. From the NMR T1/T2 ratio, where T1 is the longitudinal and T2 the transverse spin relaxation time, the relative affinity of reactant and solvent for different catalytic surfaces is determined. The catalysts with the lowest activity show a preferential surface affinity for the solvent compared to the reactant. Conversely, the catalyst with the highest activity shows a preferential surface affinity for the reactant compared to the solvent. Significantly, Ru/SiO2, which is totally inactive for the oxidation of 1,4-butanediol, exhibited a lower T1/T2 ratio (surface affinity) for 1,4-butanediol (reactant) than for a “weakly-interacting” alkane, indicating a very poor surface affinity for the diol functionality. The results provide direct evidence of the importance of the adsorbate-adsorbent interactions on catalyst activity in liquid-phase oxidations and indicate that the competitive adsorption of the solvent plays an important role in these reactions. This work demonstrates that NMR relaxation time analysis is a powerful method for comparing adsorption of liquids in porous catalysts, providing valuable information on the affinity of different chemical species for a catalyst surface. Moreover, the results demonstrate that NMR relaxation time measurements can be used not only to guide selection of solvent for use with a specific catalyst, but also selection of the catalyst itself. The results suggest that this method may be used to predict catalyst behaviour, enabling improved design and optimisation of heterogeneous catalytic processes

Maslow’s model of needs: application to Cunard and White Star marketing communications between 1900 and the 1950s

Purpose The purpose of this paper is to analyse Cunard’s marketing communications during a period of significant social and economic change. The intention is to show firstly how the company sought to meet and influence potential passengers understanding of their needs and secondly, how these would be met. Design/methodology/approach Maslow’s model of needs is used as the analytical methodology. Findings Beyond a description and review of Cunard’s marketing communications, Maslow’s model of needs is shown to provide a rationale to the company’s approach. In particular, it gives an understanding of the continued, though changing, use of images of the ship to meet the needs of different cohorts of passengers. It shows how carefully constructed images in both word and picture assuaged passengers concerns over social needs and how the company promised to meet the highest needs, whether that be for the holiday maker or the emigrant. Research Limitations During much of the period under discussion much of the advertising design work was done in house. Whilst none of these files have survived, other sources of information (for example, house magazines and internal correspondence) provide an understanding of Cunard’s attitude to its customers and the business opportunities it saw in a changing market. Where specific dates for documents are not available, a chronology of shipbuilding and use has been applied. Practical implications The paper shows how a well-established model can be used in a different way, adding to our understanding of a company adapting to changing social and economic conditions. Originality/Value As far as the author is aware this is the first time that Maslow’s model has been used explicitly as a tool to analyse marketing communication. Whilst the existing literature includes some discussion of shipping line posters visual content, there is little further discussion of their content or purpose in a changing social context. This paper provides a more structured analytical view

Deactivation studies of a carbon supported AuPt nanoparticulate catalyst in the liquid-phase aerobic oxidation of 1,2-propanediol

The aerobic oxidation of 1,2-propanediol in alkaline aqueous solvent over bimetallic AuPt/C catalysts has been studied and catalyst reusability has been assessed. A systematic decrease of catalytic conversion was observed after each reuse of the catalyst. In order to understand the causes of deactivation, the catalyst samples were characterised by N2 adsorption, temperature-programmed oxidation (TPO) and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) diffusion measurements. The results revealed that the catalyst surface area and pore volume decrease significantly after each reuse of the catalyst. The intra-particle diffusion is characterised by two distinct diffusion regimes, a fast regime with self-diffusivities of 10−9–10−11 m2 s−1 and a slow diffusion regime, with values of self-diffusivities on the order of 10−11–10−13 m2 s−1. Self-diffusivity in the fast regime is assigned to diffusion within the mesoporous space of the catalyst. Self-diffusivity in the slow diffusion region is assigned to diffusion within the microporous space and decreases after each reuse of the catalyst in a trend similar to that of pore volume, suggesting that changes in catalyst porosity and pore structure affect molecular mobility within the micropores. TPO studies of these systems showed a different distribution of oxidation products in the reused catalyst samples compared to the fresh catalyst, which suggests changes of the combustion mechanism. Altogether, the results reveal that catalyst deactivation is caused by deposition and build-up of heavy molecular species on the catalyst surface, which reduce the catalyst porosity by pore blockage and narrowing of channels, which in turn affects the diffusion rate within the micropores