Catalysis Science & Technology

Journal: Catalysis Science & Technology

Abbreviation

Catal. Sci. Technol.

Publisher

Royal Society of Chemistry

ISSN

2044-4753
2044-4761

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Publications 1 - 10 of 86

Probing coke formation during the methanol-to-hydrocarbon reaction on zeolite ZSM-5 catalyst at the nanoscale using tip-enhanced fluorescence microscopy
Bienz, Siiri; van Vreeswijk, Sophie H.; Pandey, Yashashwa; et al. (2022)
Catalysis Science & Technology
The deactivation mechanism of the widely used zeolite ZSM-5 catalysts remains unclear to date due to the lack of analytical techniques with sufficient sensitivity and/or spatial resolution. Herein, a combination of hyperspectral confocal fluorescence microscopy (CFM) and tip-enhanced fluorescence (TEFL) microscopy is used to study the formation of different coke (precursor) species involved in the deactivation of zeolite ZSM-5 during the methanol-to-hydrocarbon (MTH) reaction. CFM submicron-scale imaging shows a preferential formation of graphite-like coke species at the edges of zeolite ZSM-5 crystals within 10 min of the MTH reaction (i.e., working catalyst), whilst the amount of graphite-like coke species uniformly increased over the entire zeolite ZSM-5 surface after 90 min (i.e., deactivated catalyst). Furthermore, TEFL nanoscale imaging with ∼35 nm spatial resolution revealed that formation of coke species on the zeolite ZSM-5 surface is non-uniform and a relatively larger amount of coke is formed at the crystal steps, indicating a higher initial catalytic activity.
New and revisited insights into the promotion of methanol synthesis catalysts by CO2
Martin, Oliver; Pérez-Ramírez, Javier (2013)
Catalysis Science & Technology
Preparation of highly active phosphated TiO2 catalysts via continuous sol-gel synthesis in a microreactor
Martin, Oliver; Bolzli, N.; Puértolas, Begoña; et al. (2019)
Catalysis Science & Technology
Microreactors, featuring μm-sized tubes, offer greater flexibility and precise control of chemical processes compared to conventional large-scale reactors, due to their elevated surface-to-volume ratio and modular construction. However, their application in catalyst production has been largely neglected. Herein, we present the development of a microreactor process for the one-step sol–gel preparation of phosphated TiO2 – a catalyst which has been recently demonstrated to be an eco-friendly material for the selective synthesis of the platform chemical 5-hydroxymethylfurfural (5-HMF) from bio-derived glucose. In order to establish catalyst preparation–property–performance relationships, 18 samples were prepared according to a D-optimal experimental plan with a central point. The key properties of these samples (porosity, crystallite size, mole bulk fraction of P) were correlated, using quadratic and interaction models, with the catalytic performance (conversion, selectivity, reaction rate) of 5-HMF synthesis as a test reaction. The optimal calculated catalyst features were set as target parameters to optimise catalyst synthesis applying quadratic correlation functions. An optimal catalyst was obtained, validating the models employed, with a yield of almost 100% and a space–time yield of ca. 3 orders of magnitude higher than that of a conventional batch process (26.8 vs. 0.07 gcat h−1 cmreactor−3). The high yield could be mainly attributed to the optimal hydrolysis ratio and temperature. Controlling the TiO2 crystallite size and surface acidity in conjunction with fine-tuning of the porous properties in the microreactor led to increased glucose conversion (95.6 vs. 78.7%), surface based formation rates of 5-HMF (0.047 vs. 0.008 g5-HMF h−1 mcat−2), and selectivity towards 5-HMF (55.5 vs. 50.0%) of the optimal catalyst in relation to the batch-prepared material.
Transformations of FCC catalysts and carbonaceous deposits during repeated reaction-regeneration cycles
Almas, Qandeel; Naeem, Muhammad Awais; Baldanza, Maria Auxiliadora S.; et al. (2019)
Catalysis Science & Technology
Copper-zinc oxide interface as a methanol-selective structure in Cu-ZnO catalyst during catalytic hydrogenation of carbon dioxide to methanol
Saedy, Saeed; Newton, Mark A.; Zabilskiy, Maxim; et al. (2022)
Catalysis Science & Technology
Detailed structural and catalytic studies of ZnO/Cu/Al2O3 catalysts, aimed at deriving a better understanding of the methanol selectivity-structure relationship in the Cu-ZnO system for catalytic hydrogenation of carbon dioxide, have been conducted. Two different synthesis methods were employed, preferential chemical vapor deposition and incipient-wetness impregnation, to generate two different ZnO/Cu morphologies, which result in significantly different methanol productivity and selectivity. The incipient-wetness impregnation method results in a very high dispersion of zinc oxide over both the copper and alumina support and the subsequent formation of smaller copper particles. Preferential chemical vapor deposition deposits zinc oxide directly onto the pre-formed copper phase and yields more developed and ordered zinc oxide and copper phases. The combination of catalytic and structural (X-ray spectroscopy, X-ray diffraction, and electron microscopy) studies indicates that preferential chemical vapor deposition results in a more favorable habit of the zinc oxide in relation to the copper, which leads to more extensive formation of the ZnO-Cu interfaces required to promote the selective reduction of carbon dioxide to methanol. On the other hand, the very high dispersion of zinc oxide and copper in the impregnated sample leads to a less favorable intimacy of contact between the Cu-ZnO phases and results in a higher activity for the reverse water-gas-shift reaction, greater carbon monoxide production, and to decreased activity and selectivity for methanol production. These results, therefore, indicate that the proper contact of zinc oxide and copper phases is an essential consideration for achieving high activity and selectivity toward methanol in the Cu-ZnO system, and one that outweighs the dispersion of the reduced copper phase.
Towards environmentally benign catalytic oxidation
Baiker, Alfons; Mallat, Tamas (2013)
Catalysis Science & Technology
Synthesis factors affecting the catalytic performance and stability of Ru/C catalysts for supercritical water gasification
Peng, G.; Steib, M.; Gramm, F.; et al. (2014)
Catalysis Science & Technology
Catalytic supercritical water gasification of isopropanol (450 °C, 30 MPa) over Ru/C catalysts was carried out in a fixed-bed plug flow reactor. In the absence of Ru, isopropanol decomposed to solid carbon (coke), and H2 over the carbon support. The Ru/C catalyst was able to gasify efficiently 10 wt% isopropanol over a period of 96 h at WHSVgRu = 1228 gOrg gRu−1 h−1 with the gas composition close to the calculated thermodynamic chemical equilibrium. The catalyst lifetime was affected by the decomposition of isopropanol to solid carbon (coke) over the carbon surface that progressively filled up the pores of the activated carbon and this resulted in a covering of the Ru nanoparticles (NPs). The Ru dispersion (D) was found to be a relevant parameter. The 0.5% Ru/C (D = 0.26) was more active than the 2% Ru/C (D = 0.14). The influence of the solvent (acetone vs. water) used during the catalyst impregnation was studied and the turnover frequency (TOF) was twice as high for the Ru/C catalyst prepared with acetone. The higher Ru dispersion and the lower content of residual chloride obtained for the catalyst prepared with acetone were both responsible.
Coated sulfated zirconia/SAPO-34 for the direct conversion of CO2 to light olefins
Ramirez Galilea, Adrian; Dutta Chowdhury, Abhishek; Caglayan, Mustafa; et al. (2020)
Catalysis Science & Technology
The conversion of CO2 to light olefins via bifunctional catalysts (i.e. metal oxides/zeolites) is a promising approach to tackle CO2 emissions and, at the same time, reduce fossil-fuel dependence by closing the carbon cycle. However, designing a catalyst, especially a zeolite, that can operate at mid-low temperatures (where the selective CO2 conversion is favored) is still a challenge for the scientific community. Herein, we report the synthesis of a novel coated ZrS/SAPO-34 in combination with an iron catalyst (Fe2O3@KO2) that successfully fills this temperature gap. While making use of the properties of the zeolite to maximize light olefin selectivity, the unique nature of the sulfated zircona (ZrS) layer allows the cracking of C5+ heavy hydrocarbons produced on the Fe component at temperatures where conventional zeolites fall short. In particular, total short olefin yields per pass over 20% at CO2 conversions near 50% (total C2–C4 olefin selectivity = 40–45) can be achieved at T = 375 °C, P = 30 bar, H2/CO2 = 3 and 5000 mL g−1 h−1. Light olefin space–time yields here reported (10.4 mmol gcat−1 h−1) clearly outperform conventional zeolite based bifunctional systems for CO2 conversion.
Photobiocatalytic H2 evolution of GaN:ZnO and [FeFe]-hydrogenase recombinant Escherichia coli
Kosem, Nuttavut; Honda, Yuki; Watanabe, Motonori; et al. (2020)
Catalysis Science & Technology
The need for sustainable, renewable and low-cost approaches is a driving force behind the development of solar-to-H(2)conversion technologies. This study aims to develop a new strategy using a visible-light photocatalyst coupled to a biocatalyst for H(2)production. Photocatalytic methyl viologen (MV2+) reduction activity was investigated to discover active oxynitrides. In comparative studies with LaTiO2N, BaTaO2N and Ta3N5, it was revealed that the suitable surface area, band gap and band edge potentials are some physical factors that are responsible for the photocatalytic behaviors of GaN:ZnO in MV(2+)reduction. The activity is enhanced at higher concentrations and the alkaline pH of triethanolamine (TEOA). The expression of an active [FeFe]-hydrogenase fromEscherichia coli(Hyd(+)E. coli) as a recombinant biocatalyst was confirmed by its MV & x2d9;(+)-dependent H(2)production activity. In the photobiocatalytic system of GaN:ZnO and Hyd(+)E. coli, the rate of H(2)production reached the maximum level in the presence of MV(2+)as an electron mediator at neutral pH as a biocompatible condition. The present work reveals a novel hybrid system for H(2)production using visible-light active GaN:ZnO coupled to Hyd(+)E. coli, which shows the feasibility of being developed for photobiocatalytic H(2)evolution under solar light.
Halogen type as a selectivity switch in catalysed alkane oxyhalogenation
Zichittella, Guido; Puértolas, Begoña; Paunović, Vladimir; et al. (2018)
Catalysis Science & Technology

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