A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds

This is the peer reviewed version of the following article: A. J. Schwanke, R. Balzer, C. Wittee Lopes, D. Motta Meira, U. Díaz, A. Corma, S. Pergher, Chem. Eur. J. 2020, 26, 10459, which has been published in final form at https://doi.org/10.1002/chem.202000862. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] In this work, an MWW-type zeolite with pillars containing silicon and niobium oxide was synthesized to obtain a hierarchical zeolite. The effect of niobium insertion in the pillaring process was determined by combining a controllable acidity and accessibility in the final material. All pillared materials had niobium occupying framework positions in pillars and extra-framework positions. The pillared material, Pil-Nb-4.5 with 4.5 wt % niobium, did not compromise the mesoporosity formed by pillaring, while the increase of niobium in the structure gradually decreased the mesoporosity and ordering of lamellar stacking. The morphology of the pillared zeolites and the niobium content were found to directly affect the catalytic activity. Specifically, we report on the activity of the MWW-type zeolites with niobium catalyzing the gas-phase oxidation of volatile organic compounds (VOCs), which is an important reaction for clean environmental. All produced MWW-type zeolites with niobium were catalytically active, even at low temperatures and low niobium loading, and provided excellent conversion efficiencies.A.J.S. thanks the CordenacAo de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (CAPES)-Finance Code 001, the PDSE program (process number 99999.004779/2014-02) and the prof. Claudio Radtke from the PPGQ-UFRGS for the XPS analyses. C.W.L. is grateful to INOMAT/CAPES for a postdoctoral fellowship. U.D. thanks the funding by the Spanish Government (MAT2017-82288-C2-1-P).Schwanke, AJ.; Balzer, R.; Lopes, CW.; Meira, DM.; Díaz Morales, UM.; Corma Canós, A.; Pergher, S. (2020). A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds. Chemistry - A European Journal. 26(46):1-12. https://doi.org/10.1002/chem.202000862S1122646Zhang, X., Guo, J., Guan, P., Liu, C., Huang, H., Xue, F., … Chisholm, M. F. (2013). Catalytically active single-atom niobium in graphitic layers. Nature Communications, 4(1). doi:10.1038/ncomms2929Yan, W., Zhang, G., Yan, H., Liu, Y., Chen, X., Feng, X., … Yang, C. (2018). Liquid-Phase Epoxidation of Light Olefins over W and Nb Nanocatalysts. ACS Sustainable Chemistry & Engineering, 6(4), 4423-4452. doi:10.1021/acssuschemeng.7b03101Ziolek, M., & Sobczak, I. (2017). The role of niobium component in heterogeneous catalysts. 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Chemical gradients in automotive Cu-SSZ-13 catalysts for NOx_{x} removal revealed by operando X-ray spectrotomography

NOx emissions are a major source of pollution, demanding ever improving performance from catalytic aftertreatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model rather than technical catalysts, and global rather than spatially-resolved characterisation tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform 3D chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NO$_{x}$ reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NOx reduction with adsorption-desorption of NH$_{3}$ and mass transport phenomena, were revealed with micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct 3D visualisation of complex reactions on nonmodel catalysts is only feasible using operando X-ray spectrotomography, which can improve our understanding of structure-activity relationships including the observation of mass and heat transport effects

"Insights into structure and surface properties of cerium promoted- platinum catalysts addressed by in situ techniques under water gas shift reaction"

Pt based catalysts were measured with in situ X ray absorption fine structure spectroscopy (XAFS) to obtain information about the catalyst crystalline structure and electronic properties as a function of catalyst composition, method of preparation, inlet feed conditions and temperature. In these experiments, two type of catalysts were studied: i) nanoparticles of Pt occluded in Al2O3 or CeO2-Al2O3 matrix containing 1.5 % of Pt where two different methods to incorporate the cerium were used and ii) conventional Pt supported catalysts containing 0.3 and 1 % of Pt on Al2O3 or with addition of 6 or 12 % of ceria. For catalysts based on nanoparticles, XAFS spectra were acquired at Pt L3-edge and Ce K and L3-edge under reduction and water gas shift (WGS) reaction conditions. The XAFS results reveal, after the reduction, the presence of Pt nanoparticles with similar coordination numbers (NPt-Pt), about 6, and similar Pt-Pt distances, about 2.75  0.01 Å. The catalyst activity for WGS and the strength of interaction between the metal and the support are related with cerium oxide structure revealed by XAFS analysis at Ce K and L3 edges. In situ infrared spectroscopy under WGS conditions revealed the presence of formates on the catalyst surface and that they are probably spectators for the reaction. It was possible to observe that these catalysts changes according to the atmosphere and temperature. Thus, it was possible to demonstrate, using the pre-formed nanoparticles that several parameters affect the catalyst behavior like: the metallic and the oxide particle size, the contact between them and what is exposed on the surface. For the conventional catalysts, the addition of ceria on 03PtAl sample enhances Pt oxidation, reflecting in a larger Pt-O coordination number for this sample. After reduction, 03PtAl resulted in larger Pt particles compared to the 12Ce03PtAl. For Ce-containing samples, in addition to the Pt-Pt contribution, a Pt-O contribution had to be considered to fit the spectra. This Pt-O increases proportionally to the cerium amount demonstrating that Pt clusters are anchored on support through a Pt-O bond. The Pt structure changes depends on the temperature, support nature and reactants composition, demonstrating that the catalytic properties requires the use of in situ characterization techniques.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Catalisadores de Pt foram preparados, informações estruturais e eletrônicas foram obtidas usando espectroscopia da estrutura fina de absorção de raios X (XAFS) em função da composição do catalisador, método de preparação, composição da atmosfera e temperatura. Dois tipos de catalisadores foram estudados: i) catalisadores sintetizados com nanopartículas de Pt (1,5% de Pt) ocluídas em uma matrix de Al2O3 ou CeO2-Al2O3. Neste estudo, dois métodos de preparação para incorporação do cérioforam utilizados e ii) catalisadores de Pt convencionais com 0,3 ou 1% de Pt em Al2O3 e ainda com a adição de céria 6 ou 12%. Para os catalisadores baseados em nanopartículas, os experimentos de XAFS foram realizados na borda L3 da Pt e nas bordas L3 e K do Ce sob atmosfera de redução e condições de reação de deslocamento gás-água (WGS). Os resultados de XAFS, após a redução, revelaram a presença de nanopartículas com número de coordenação (NPt-Pt) similares, em torno de 6, e distância Pt-Pt em torno de 2.75  0.01 Å, para todas as amostras. A atividade catalítica e a intensidade da interação metal-suporte estão relacionadas com a estrutura do óxido de cério revelada através das análise de XAFS nas bordas K e L3 do Ce. Medidas de infravermelho in situ revelaram a presença de formiatos na superfície do catalisador e que esses são provavelmente espectadores da reação. Foi possível observar que estes catalisadores mudam segundo a atmosfera e a temperatura. Assim, foi possível demonstar, usando as nanopartículas de platina, que diversos parâmetros afetam o comportamento do catalisador como: o tamanho do domínio cristalino do óxido, o contato entre o metal e o óxido e os sítios ativos expostos na superfície. Para os catalisadores convencionais, as amostras contendo cério apresentaram-se mais oxidadas do que as amostras de platina-alumina; estas após tratamento em alta temperatura aglomeraram. No ajuste dos espectros de EXAFS, para as amostras contendo Ce, foi necessário incluir a contribuição Pt-O além da contribuição Pt-Pt. Essa contribuição Pt-O aumentou proporcionalmente à concentração de Ce demonstrando o ancoramento da Pt ao suporte através dessa ligação. A estrutura da Pt mudou de acordo com a temperatura, o suporte e composição dos reagentes na atmosfera demonstrando a importante ferramenta que são as técnicas de caracterização in situ para o entendimento das propriedades catalíticas.FAPESP: 2010/52291-

Rh2P Nanoparticles Stabilized by Carbon Patches for Hydroformylation of Olefins

[EN] Rh2P nanoparticles (NPs) have been identified as suitable mimics of [Rh-I(Ph3P)(3)](+), the benchmark of homogeneous catalysts in liquid-phase hydroformylation. For this reason, a fitted synthetic strategy is required to develop catalysts based exclusively on Rh2P NPs. To attain this, two synthetic pathways have been devised. In the first one, two separate sources of Rh and P were used. In the second one, the Wilkinson complex was employed as a unique source of Rh and P to probe the positive influence of the well-defined molecular organization on the preparation of dispersed and controlled Rh2P nanoparticles, stabilized by carbon patches formed during the pyrolysis treatment from PPh3. In addition, metallic Rh nanoparticles were also synthesized to be used as reference. All catalysts have been compared by means of: transmission electron microscopy, Xray diffraction, and X-ray adsorption spectroscopy. The application of XAS to the study of Rh2P NPs is unusual and has been essential in the discussion of the results. Starting with a well-defined metal precursor leads to the exclusive formation of Rh2P NPs with excellent catalytic activity for the liquid-phase hydroformylation. The role of P is to modulate the particle size and the electronic configuration of Rh species, resulting in the improvement of the catalytic performance and the obtention of turnover frequencies of 5236 h(-1) at 60 degrees C and 17,788 h(-1) at 100 degrees C.Program Severo Ochoa SEV-2016-0683 is gratefully acknowledged. C.G.-R. thanks MINECO for her FPU Ph.D. contract FPU17/04172. The authors thank the financial support by the Spanish Government (RTI2018-096399-A-I00). The authors thank J.G.M. for his technical support. We also thank the Electron Microscopy Service of the UPV for TEM facilities. C.W.L. thanks PRH 50.1 - ANP/FINEP Human Resources Program for the Visiting Researcher Fellowship. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by the Argonne National Laboratory and was supported by the U.S. DOE under contract no. DE-AC02-06CH11357 and the Canadian Light Source and its funding partners.Galdeano-Ruano, CP.; Wittee Lopes, C.; Motta Meira, D.; Corma Canós, A.; Oña-Burgos, P. (2021). Rh2P Nanoparticles Stabilized by Carbon Patches for Hydroformylation of Olefins. ACS Applied Nano Materials. 4(10):10743-10753. https://doi.org/10.1021/acsanm.1c02194S107431075341

Sample Environment for Operando Hard X-ray Tomography—An Enabling Technology for Multimodal Characterization in Heterogeneous Catalysis

Structure–activity relations in heterogeneous catalysis can be revealed through in situ and operando measurements of catalysts in their active state. While hard X-ray tomography is an ideal method for non-invasive, multimodal 3D structural characterization on the micron to nm scale, performing tomography under controlled gas and temperature conditions is challenging. Here, we present a flexible sample environment for operando hard X-ray tomography at synchrotron radiation sources. The setup features are discussed, with demonstrations of operando powder X-ray diffraction tomography (XRD-CT) and energy-dispersive tomographic X-ray absorption spectroscopy (ED-XAS-CT). Catalysts for CO$_2$ methanation and partial oxidation of methane are shown as case studies. The setup can be adapted for different hard X-ray microscopy, spectroscopy, or scattering synchrotron radiation beamlines, is compatible with absorption, diffraction, fluorescence, and phase-contrast imaging, and can operate with scanning focused beam or full-field acquisition mode. We present an accessible methodology for operando hard X-ray tomography studies, which offer a unique source of 3D spatially resolved characterization data unavailable to contemporary methods

Oxygen step-response experiments for methane oxidation over Pd/Al2O3: An in situ XAFS study

Methane oxidation over Pd/Al2O3 has been investigated by in situ XAFS characterization during oxygen step-response experiments. With a net-reducing feed gas, Pd is in a reduced state and the introduction of oxygen leads to oxidation of palladium as well as increased methane conversion. When the rate of Pd oxidation is slow, a transient surface oxidized state is observed with low activity for methane oxidation. The activity increases when palladium is further oxidized and the highest activity is observed for palladium oxide

CO Hydrogenation on Cobalt-Based Catalysts: Tin Poisoning Unravels CO in Hollow Sites as a Main Surface Intermediate

International audienceSite poisoning is a powerful method to unravel the nature of active sites or reaction intermediates. The nature of the intermediates involved in the hydrogenation of CO was unraveled by poisoning alumina-supported cobalt catalysts with various concentrations of tin. The rate of formation of the main reaction products (methane and propylene) was found to be proportional to the concentration of multi-bonded CO, likely located in hollow sites. The specific rate of decomposition of these species was sufficient to account for the formation of the main products. These hollow-CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions used here, while linear CO are mostly spectators

Structure and reactive properties of Nb-impregnated two-dimensional pillared MWW zeolites for total oxidation of volatile organic compounds

[EN] In this work, the structure and reactive properties of niobium (Nb)-impregnated MWW-type materials were evaluated for gas-phase total oxidation of volatile organic compounds, including BTX (benzene, toluene and o -xylene). The role of the type of structure (two or three-dimensional) and the loading of Nb were considered. The results indicated most Nb species with a tetrahedral coordination on the external surfaces of both two- and threedimensional zeolites, together with a minimal contribution of octahedral extra-framework Nb2O5 species. The texture and Nb content played a key role in the gas-phase total oxidation of BTX. With the same Nb content (5 wt %), the pillared zeolite exhibited a higher specific surface, larger pore volume and mesopores between the MWW nanosheets when compared to the MCM-22 zeolites, which resulted in high accessibility of the reactant molecules to the active sites, reflected in higher BTX conversion at lower and higher temperatures (50-300 degrees C). The best performance was achieved with the pillared zeolite (10 wt% Nb), reaching a BTX conversion at 300 degrees C of 92%, 69% and 58%, respectively. The catalyst was stable for up to 30 h of reaction.A.J.S. thanks the Cordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES, Brazil; Finance Code 001) and the Programa de Pos-Graduacao em Quimica of the Universidade Federal do Rio Grande do Sul (PPGQ-UFRGS) . C.W.L. thanks the PRH 50.1 - ANP/FINEP Human Resources Program for the Visiting Researcher Fellowship. This research used resources of the Advanced Photon Source, a user facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357 and by the Canadian Light Source and its funding partners. U.D thanks the MAT2017-82288-C2-1-P Project.A. Schwanke; RB; Wittee Lopes, C.; Debora Motta Meira; Díaz Morales, UM.; Sibele B. Pergher; Katia Bernardo-Gusmao (2021). Structure and reactive properties of Nb-impregnated two-dimensional pillared MWW zeolites for total oxidation of volatile organic compounds. Microporous and Mesoporous Materials. 327:1-11. https://doi.org/10.1016/j.micromeso.2021.111425S11132

Watching Kinetic Studies as Chemical Maps Using Open-Source Software

A nonproprietary software package, “PyMca”, primarily developed for X-ray fluorescence analysis offers an easy-to-use interface for calculating maps, by integrating intensity (of X-ray fluorescence, as well as any spectral data) over Regions Of Interest (ROI), by performing per pixel operations or by applying multivariate analysis. Here we show that, while initially developed to analyze hyperspectral two-dimensional (spatial) maps, this tool can be beneficial as well to anyone interested in measuring spectral variations over one or two dimensions, these dimensions being time, temperature, and so on. Different possibilities offered by the software (preprocessing, simultaneous analysis of replicas, of different conditions, ROI calculation, multivariate analysis, determination of reaction rate constant and of Arrhenius plot) are illustrated with two examples. The first example is the Fourier transform infrared spectroscopy (FTIR) follow-up of the saponification of oil by lead compounds. The disappearance of reagent (oil) and formation of products (lead carboxylates and glycerol) can be easily followed and quantified. The second example is a combined extended X-ray absorption fine structure (EXAFS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and mass spectroscopy (MS) analysis of RhAl₂O₃ catalyst under NO reduction by CO in the presence of O₂. It is possible to appreciate, in a single shot, Rh particles’ structure and surface changes and gas release and adsorption in the reaction conditions

Structure–function relationship during CO2\mathrm{CO_{2}} methanation over Rh/Al2O3\mathrm{Rh/Al_{2}O_{3}} and Rh/SiO2\mathrm{Rh/SiO_{2}} catalysts under atmospheric pressure conditions

The effect of the support material and chemical state of Rh in Rh/A$_2$O$_3$ and Rh/SiO$_2$ model catalysts during CO$_2$ hydrogenation were studied by a combined array of in situ characterisation techniques including diffuse reflectance infrared Fourier transform spectroscopy, energy-dispersive X-ray absorption spectroscopy and high-energy X-ray diffraction at 250–350 °C and atmospheric pressure. CO$_2$ methanation proceeds via intermediate formation of adsorbed CO species on metallic Rh, likely followed by their hydrogenation to methane. The linearly-bonded CO species is suggested to be a more active precursor in the hydrogenation compared to the bridge-bonded species, which seems to be related to particle size effects: for larger particles mainly the formation of inactive bridge-bonded CO species takes place. Further, analysis of the chemical state of Rh under the reaction conditions reveal a minor formation of RhOx from dissociation of CO$_2$, which is a consequence of the increased activity observed over the Rh/Al$_2$O$_3$ catalyst