Showing papers by "Jacob A. Moulijn published in 2013"

Elucidation and Evolution of the Active Component within Cu/Fe/ZSM-5 for Catalytic Methane Oxidation: From Synthesis to Catalysis

Abstract: The development of a catalytic, one-step route for the oxidation of methane to methanol remains one of the greatest challenges within catalysis. Of particular importance is the need to develop an efficient route that proceeds under mild reaction conditions so as to avoid deeper oxidation and the economic limitations of the currently practiced syngas route. Recently, it was demonstrated that a copper- and iron-containing zeolite is an efficient catalyst for such a one-step process. The catalyst in question (Cu–Fe–ZSM-5) is capable of selectively transforming methane to methanol in an aqueous medium with hydrogen peroxide as the terminal oxidant. Nevertheless, despite its high activity and unparalleled methanol selectivity, the origin of its activity and the precise nature of its active species are not yet fully understood. Through a combination of catalytic and spectroscopic studies, we hereby demonstrate that extraframework Fe species are the active component of the catalyst for methane oxidation, although the speciation of these sites from synthesis to catalysis significantly alters the observed activity and selectivity. The analogies and differences between this system and other iron-containing zeolite-catalyzed processes, such as N2O-mediated benzene hydroxylation, are also considered.

Effect of Reaction Conditions on the Direct Synthesis of Hydrogen Peroxide with a AuPd/TiO2 Catalyst in a Flow Reactor

Abstract: The direct synthesis of hydrogen peroxide (H2O2) represents a potential alternative to the currently industrially used anthraquinone process, and Au–Pd catalysts have been identified as effective catalysts. To obtain a direct process, a detailed understanding of the reaction conditions in a continuous flow system is needed. In this study, we use a flow reactor to study reaction conditions independently, including total gas flow rate, catalyst mass, reaction pressure, solvent flow rate, and H2/O2 molar ratio. The study was carried out without the addition of any halide or acid additives often used to suppress the sequential hydrogenation and decomposition reactions that allowed the kinetics of these reactions to be studied along with the synthesis reaction. A global kinetic model describing the net and gross synthesis rate is proposed, and on the basis of this model, we propose that the decomposition reaction suppresses the production of H2O2 to a greater extent than hydrogenation and that catalyst design ...

Aqueous-Phase Methane Oxidation over Fe-MFI Zeolites; Promotion through Isomorphous Framework Substitution.

Abstract: Fe and Cu-containing zeolites have recently been shown to be efficient catalysts for the one-step selective transformation of methane into methanol in an aqueous medium at only 50 oC, using H2O2 as green oxidant. Previously, we have observed that Fe species alone are capable of catalysing this highly selective transformation. However, further catalytic testing and spectroscopic investigations demonstrates that although these extra-framework Fe species are the active component of the catalyst, significant promotion is observed upon the incorporation of other trivalent cations e.g. Al3+, Ga3+, into the MFI-framework. Whilst these additional framework species do not constitute active catalytic centres, promotion is observed upon their incorporation as they (1) facilitate the extraction of Fe from the zeolite framework, and hence increase the formation of the active Fe species, and (2) provide an associated negatively-charged framework, which is capable of stabilizing and maintaining the dispersion of the cationic extra-framework Fe species responsible for catalytic activity. By understanding these phenomena, and subsequently controlling the overall composition of the catalyst (Fe and Al), we have subsequently been able to prepare a catalyst of equal intrinsic activity (i.e. TOF) but five-times higher productivity (i.e. space-time-yield) to the best catalysts reported for this reaction to date.

Catalyst Performance Testing in Multiphase Systems: Implications of Using Small Catalyst Particles in Hydrodesulfurization

Abstract: Three different gas–liquid–solid reactor configurations have been used to investigate the performance of a P-doped NiMo/Al2O3 catalyst in the hydrodesulfurization of dibenzothiophene. The commonly used millipacked bed reactor with 250–500 μm catalyst particles diluted with 125 μm inert particles, a micropacked bed reactor with 55–90 μm catalyst particles, and a slurry reactor with 150–250 μm catalyst particles were used in the catalyst performance testing program. It appeared that the inherently small particle size in the packed beds causes the hydrodynamics to be dramatically different compared to the industrially applied trickle-bed reactors. For particles smaller than typically 2 mm the capillary forces predominate over the viscous and gravitational forces, in sharp contrast to large-scale industrial reactors. Since the gas flow follows preferential pathways through beds consisting of small particles, the poor radial dispersion of the gaseous components can cause mass-transport limitations, even for a rather slow reaction such as the hydrodesulfurization (HDS) of dibenzothiophene, as a result of the strong inhibition by the reaction product H2S. An adapted criterion is proposed for estimation of the contribution of poor radial dispersion in catalyst performance testing.

Monolithic reactors in catalysis: excellent control

Abstract: Structured reactors offer high precision in catalysis at all relevant length scales of the catalytic process, from the catalytic species up to the reactor. They offer unusual freedom in design with respect to diffusion length, hydrodynamic regime and reactor configuration. Monoliths are the prime example of such systems.

Isolation of anhydro sugar alcohols by selective adsorbents

Abstract: A method is disclosed for recovering anhydrosugar alcohols from a mixture comprising closely related compounds, such as sugar alcohols. In the method the mixture is contacted with an adsorbent, whereby the anhydrosugar alcohols are selectively adsorbed. The anhydrosugar alcohols can be recovered by desorption from the adsorbent, using a desorbing solvent.