Technical Catalysts Research Articles

Applications of Neutron Scattering in Technical Catalysis: Characterisation of Hydrogenous Species on/in Unsupported and Supported Palladium

Recent results from inelastic neutron scattering (INS) measurements are reviewed that show the synergy between research on hydrogen adsorption/absorption on/in catalysts and chemical engineering. The proton dynamics of catalysts for large scale reactor technology are compared. The focus is the identification and quantification of hydrogenous species on, and inside, fresh, hydrogenated and dehydrogenated palladium black and supported palladium catalysts of different particle size, type of support and, therefore, morphology. INS studies of in-situ hydrogenation/ dehydrogenation of catalysts of 25–60 g size per sample are carried out in stainless steel cans as a function of varying hydrogen pressures. Differences in hysteresis effects in retaining hydrogen inside the catalyst in desorption from palladium hydrides and hydrogen bonding in adsorption sites in varying particle morphologies on different supports were evaluated. This aids the understanding of hydrogen/palladium interactions in catalytic processes with varying local hydrogen partial pressure, e.g. in loop reactors. The importance of the measured on-top Pd–H site in catalytic hydrogenation reactions is discussed together with previous INS results on the degree of deactivation of a technical catalyst by molecular blocking of the on-top site.

Valorisation of a lignin-rich residue via catalytic pyrolysis over ZrO2/ZSM-5 technical catalyst

The thermochemical valorisation of a lignin-rich residue has been investigated by thermal and catalytic pyrolysis. The catalyst, based on nanocrystalline ZSM-5, has been modified with ZrO2 and agglomerated with attapulgite (ZrO2/n-ZSM-5-ATP). Firstly, the effect of the temperature in thermal pyrolysis has been explored, establishing 600 °C as the optimal temperature to thermally decompose the lignin-rich feedstock, yielding 53.7 wt% of bio-oil* (water-free bio-oil). In contrast, the incorporation of the technical catalyst using an ex-situ reactor, as well as the increase in the catalyst/lignin ratio, strongly affected the mass and energy yields of products. Thus, a significant decrease of the bio-oil* yield was observed, although its composition was significantly improved, with a reduction of the oxygen content from 30 to 10 wt%. Comparing the parent zeolite with the technical catalyst, the latter afforded a bio-oil* production with lower oxygen content, a higher share of aromatics and lower concentration of heavy species (non-detected by GC–MS). In particular, the technical catalyst allows increasing the concentration in bio-oil* of GC–MS detected compounds, which are the most valuable for commercial applications, by a factor of 2.5 regarding the thermal test. Interestingly, these remarkable results are obtained despite working under mild catalytic conditions (450 °C, catalyst/lignin = 0.2 g/g).

Catalytic Fast Pyrolysis of Biomass: Catalyst Characterization Reveals the Feed-Dependent Deactivation of a Technical ZSM-5-Based Catalyst

Catalyst deactivation due to coking is a major challenge in the catalytic fast pyrolysis (CFP) of biomass. Here, a multitechnique investigation of a technical Al2O3-bound ZSM-5-based extrudate catalyst, used for the CFP of pine wood and cellulose (at a reactor temperature of 500 °C), provided insight into the effects of extrusion, the catalytic pyrolysis process, and catalyst regeneration on the catalyst structure. As a result of a reduction in acidity and surface area due to the coking catalyst, the activity dropped drastically with increasing time-on-stream (TOS), as evidenced by a decrease in aromatics yield. Strikingly, confocal fluorescence microscopy at the single-particle level revealed that vapor components derived from whole biomass or just the cellulose component coke differently. While pine-wood-derived species mainly blocked the external area of the catalyst particle, larger carbon deposits were formed inside the catalyst’s micropores with cellulose-derived species. Pyridine FT-IR and solid-state NMR spectroscopy demonstrated irreversible changes after regeneration, likely due to partial dealumination. Taken together with <30 g kg–1 aromatics yield on a feed basis, the results show a mismatch between biomass pyrolysis vapors and the technical catalyst used due to a complex interplay of mass transfer limitations and CFP chemistry.

Chemical gradients in automotive Cu-SSZ-13 catalysts for NOx removal revealed by operando X-ray spectrotomography

Nitrogen oxide (NOx) emissions are a major source of pollution, demanding ever-improving performance from catalytic after-treatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model catalysts rather than technical catalysts, and by global rather than spatially resolved characterization tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform three-dimensional chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NOx reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NOx reduction with adsorption–desorption of NH3 and mass transport phenomena, were revealed at micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct three-dimensional visualization of complex reactions on non-model catalysts is feasible only by the use of operando X-ray spectrotomography, which can improve our understanding of structure–activity relationships, including the observation of mass and heat transport effects. Obtaining spatially resolved spectroscopic information for catalysts under working conditions remains challenging. Here, an approach that combines X-ray absorption spectroscopy with microtomography is introduced and showcased for the selective catalytic reduction of NOx with ammonia over a Cu-SSZ-13 washcoated monolith catalyst.

Evidence of Octahedral Co–Mo–S Sites in Hydrodesulfurization Catalysts as Determined by Resonant Inelastic X-ray Scattering and X-ray Absorption Spectroscopy

Fundamental understanding of the active sites in CoMo/Al2O3 catalysts is crucial to improve the production of clean transportation fuels by hydrodesulfurization (HDS). In this work, the coordination state and number of active sites (“Co–Mo–S”) in sulfided CoMo/Al2O3 catalysts prepared with and without chelating additives were determined using in situ 1s2p resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS). Based on the evaluation of thiophene HDS activity as a function of the Co/Mo ratio, it was determined that only for Co/Mo < 0.1, cobalt is exclusively in interaction with the MoS2 phase, making these compositions ideal for identifying the nature of the active cobalt sites for hydrogenolysis. These cobalt promoter atoms were in centrosymmetric coordination with the MoS2 phase, with six sulfur ligands coordinated to each cobalt center. The octahedral coordination of cobalt in Co–Mo–S in alumina-supported HDS catalysts contrasts the tetrahedral cobalt coordination found in Co-promoted MoS2 model systems supported on gold or carbon. We attribute the difference to more disordered MoS2 structures in technical alumina-supported HDS catalysts. The number of Co–Mo–S sites depended strongly on the catalyst preparation method. Chelating additives, such as citric acid and nitrilotriacetic acid, increased the number of Co–Mo–S sites without significantly altering their intrinsic activity. These results demonstrate that the state-of-the-art structural characterization tools, such as RIXS, identify the structure of active sites in actual catalysts and that these structures may be different from model systems. Combining such characterization tools with guided catalyst design can provide an insight into the structure of amorphous, nanostructured materials, which aid in the development of improved heterogeneous catalysts. KEYWORDS:Hydrodesulfurization Co−Mo−S RIXS active site XAS

Shaped Hierarchical H-ZSM-5 Catalysts for the Conversion of Dimethyl Ether to Gasoline

Hierarchical H-ZSM-5 zeolites are a promising class of heterogeneous catalysts that have shown encouraging results in lab-scale studies for the production of gasoline from dimethyl ether (DTG conversion). However, the influences of mesopore formation and shaping on various catalyst properties are still under debate. In this study, a series of H-ZSM-5 zeolites with hierarchical pore structures were prepared by modifying commercially available zeolites via alkaline treatment (“desilication”). The powdered zeolites were shaped into technical catalyst bodies by wet extrusion using either silica or alumina binders. All materials were extensively characterized. The different interactions during alkaline treatment were related to the observed modifications in the zeolite properties of the materials obtained. Although many properties of modified and untreated zeolite powders remained predominantly unchanged in their shaped catalyst equivalents, both binders affected certain material characteristics, particularly those related to their acidity. Finally, preliminary tests showed enhanced catalytic performance of hierarchical ZSM-5 catalysts in DTG conversion.

Enhanced Direct Dimethyl Ether Synthesis from CO2-Rich Syngas with Cu/ZnO/ZrO2 Catalysts Prepared by Continuous Co-Precipitation

The manufacturing of technical catalysts generally involves a sequence of different process steps, of which co-precipitation is one of the most important. In this study, we investigate how continuous co-precipitation influences the properties of Cu/ZnO/ZrO2 (CZZ) catalysts and their application in the direct synthesis of dimethyl ether (DME) from CO2/CO/H2 feeds. We compare material characteristics investigated by means of XRF, XRD, N2 physisorption, H2-TPR, N2O-RFC, TEM and EDXS as well as the catalytic properties to those of CZZ catalysts prepared by a semi-batch co-precipitation method. Ultra-fast mixing in continuous co-precipitation results in high BET and copper surface areas as well as in improved metal dispersion. DME synthesis performed in combination with a ferrierite-type co-catalyst shows correspondingly improved productivity for CZZ catalysts prepared by the continuous co-precipitation method, using CO2-rich as well as CO-rich syngas feeds. Our continuous co-precipitation approach allows for improved material homogeneity due to faster and more homogeneous solid formation. The so-called “chemical memory” stamped during initial co-precipitation is kept through all process steps and is reflected in the final catalytic properties. Furthermore, our continuous co-precipitation approach may be easily scaled-up to industrial production rates by numbering-up. Hence, we believe that our approach represents a promising contribution to improve catalysts for direct DME synthesis.

First Order Kinetics of Biodiesel Synthesis Using Used Frying Oil through Transesterification Reaction

This research aims to study the first-order kinetics of biodiesel production from used frying oil (UFO) through transesterification with methanol. Used frying oil was collected from fried peddlers around the campus of the University of Lampung. Technical grade methanol and NaOH catalyst were purchased from a local chemical supplier. The experiment was carried out with 100 ml of UFO at various combinations of oil to methanol molar ratio (1:4, 1:5, and 1:6), reaction temperatures(30 to 55oC, the ramping temperature of 5o C), and reaction time of 0.25 to 10 minutes. First-order kinetic was employed using 126 data pairs (87.5%). The acquired kinetic model was validated using 18 data sets (12.5%) observed at a reaction time of eight min. Results show that biodiesel yield was increased with reaction time, its molar ratio, and temperature. The maximum return of 78.44% was achieved at 55oC and molar ratio of 1:6. The kinetic analysis obtains the reaction rate constant (k) in the range of 0.045 to 0.130. The value of k increases with the reaction temperature and molar ratio. The analysis also reveals the average activation energy (Ea) of the UFO transesterification reaction with methanol and NaOH catalyst to be 21.59 kJ/mol. First-order kinetic is suitable to predict biodiesel yield from UFO because of low %RMSE (3.39%) and high R2 (0.8454

Mesolevel Bifunctional Catalysis

The review is focused on requirements for technical bifunctional catalysts containing, in addition to a metal phase and an acid support (zeolite), various components required for providing an effective heat and mass transfer and chemical or mechanical functions. Some catalytic reactions in which these components (e.g., a binder for extrusion) affect catalytic properties are discussed. A strategy of introducing metals into a shaped catalyst by deposition either on a zeolite or a binder, which affects the distance between the sites of various types and the catalytic properties of the resulting extrudates, is described.

Perspectives on Computational Catalysis for Metal Nanoparticles

Understanding reaction kinetics over metal-nanoparticles is central in technical catalyst design. In this Perspective, we compare computational methods to analyze and model reaction kinetics on metal nanoparticles. We discuss energy-barrier and Sabatier analysis, mean-field microkinetic modeling, and kinetic Monte Carlo simulations. By explicit simulations, we show that reactions on metal-nanoparticles are characterized by long-range kinetic couplings, which requires methods that consider coupled site-assemblies. In light of these observations, extended model surfaces may not capture the complexity of nanoparticle-kinetics, and arguments about catalytic performance relying on single energy barriers may be insufficient.

Revealing the active species of Cu-based catalysts for heterogeneous Fenton reaction

Cu-based heterogeneous Fenton catalysts are promising for industrial wastewater treatment, nevertheless it remains a great challenge to understand the catalytic mechanism due to the difficulty in identifying the critical roles of coexisting Cu0, Cu+ and Cu2+ species in the technical catalysts. In order to identify the catalytic roles of various copper species, core-shell Cu@SiO2 catalysts reduced at different reduction temperatures were studied for rhodamine B degradation. The Cu+ dominating catalyst, Cu@SiO2-R200, exhibited the highest degradation rate with more than 95% RhB (10 ppm) removal within 10 min. Combined with multiple techniques, including in situ spectroscopy, and density functional theory calculations, it can be concluded that Cu+ acts as the primary active species with the highest efficiency in activating the H2O2 to produce ·OH and subsequently degrading the contaminants. In this work, the structure-performance relationship of Cu-based heterogeneous Fenton reaction was elucidated to inspire the rational design of high-performance heterogeneous catalysts.

The Framework for Seeking Alpha in the Global Securitization Market

A decade has passed since the global financial crisis. The securitization market gradually recovered not only in the US, but globally. The securitization market is becoming more international, with explosive growth in the Chinese ABS market, which competes with the more established securitization markets in the US, Europe, and Australia for capital. The worldwide securitization market offers tremendous alpha generating opportunities for investors. In order to achieve the highest total return through optimal portfolio positioning, global bond investors need to compare and evaluate the relative value of investment opportunities constantly in those markets. In making their investment decisions, investors are recommended to follow a dynamic framework centered around a four-pillar analysis of asset fundamentals, valuation anomalies, market technical, and macro catalysts. This article illustrates how investors can identify values in these markets by applying this dynamic framework in three case studies of attractive opportunities in Spain, the US, and China. TOPICS:Asset-backed securities (ABS), emerging markets, portfolio management/multi-asset allocation, performance measurement

Optimization of nickel and ceria catalyst content for synthetic natural gas production through CO2 methanation

Manufacturing of catalysts with high reaction rates at mild conditions is important for an efficient production of synthetic natural gas through the CO2 methanation process. In this work, the design of a technical catalyst based on an optimal content of Ni as active phase, CeO2 as promoter and γ-Al2O3 micro-spheres as support (dp = 400–500 μm) is evaluated. The systematic optimization of Ni, CeO2 and γ-Al2O3 content revealed that a proper balance of the positive effects that each component provided individually, was found at 25 wt% Ni, 20 wt% CeO2 and 55 wt% γ-Al2O3 content. This catalyst was stable for 120 h at 300 °C. The high loading of CeO2 is far from the classical definition of promoter and it covers the gap between the addition in a low amount as promoter and its uncompetitive use as bulk support. The highest catalytic activity was attributed to high metallic surface area (5 m2·g−1), high nickel reducibility (79% at 500 °C) and the formation of moderate basic sites that can adsorb CO2 (−65 kJ·molCO2−1). In comparison with similar research catalysts and a commercial reference, the optimum formation showed higher activity for synthetic natural gas production. Therefore, the micro-catalyst can be implemented in the micro-structured reactors that are available in the market.

Production and testing of technical catalysts based on MnO2 for the abatement of aromatic volatile compounds at the laboratory and pilot plant scales

Abstract Shaping is a crucial step to produce technical catalysts that remains as some sort of dark art for catalytic researchers in academia. This contribution discusses aspects concerning the fabrication of technical catalysts based on MnO2 powders aimed for the combustion of hazardous aromatic compounds; namely, benzene and styrene. Both laboratory and pilot plant scale catalytic tests were done over tablets and extrudates of MnO2. Key physicochemical properties of these materials; namely, surface area, porosity, crystallinity, and mechanical resistance, were assessed and correlated to the catalytic behaviour. On the one hand, the paper describes the hurdles to be overcome when formulating and testing a technical catalyst whose characteristics must be a good compromise between its physicochemical properties and catalytic behaviour at the pilot plant scale. Furthermore, the importance of adopting adequate security and waste management protocols for testing technical catalysts is highlighted. On the other hand, the following conclusions were drawn from the analysis of results: (i) Between tableting and extrusion, only the latter was found to produce shaped bodies with suitable mechanical resistance for pilot plant scale tests. (ii) Calcination of the fabricated extrudates at temperatures from 500 °C leads to a crystallographic transformation of the MnO2 that had a positive impact on the intrinsic activity of the technical catalyst while favouring its mechanical resistance owing to densification at the expense of a decrease in surface area and enlargement of pore size distribution. (iii) Thanks to pilot plant testing of the catalysts, it was possible to identify a detailed reaction scheme for styrene combustion in which besides the occurrence of oxidation, reactions of hydrogenation, dehydrogenation, ring opening, and isomerization take place by a combination of both surface and free radical mechanisms.

Metal-oxide promoted Ni/Al2O3 as CO2 methanation micro-size catalysts

The Power-to-Gas concept has the challenge to convert the excess of renewable electricity to synthetic natural gas, composed mainly by methane, through CO2 methanation. The superior heat transfer capacity of micro-structured reactors offers a suitable alternative for an efficient control of the reaction temperature. In the present work, the strategy of adding large amount of metal oxide promoters (15 wt.%) to nickel supported on micro-size catalysts (dp = 400–500 μm) is presented. The addition of CeO2, La2O3, Sm2O3, Y2O3 and ZrO2 was clearly beneficial, as the corresponding metal-oxide promoted catalysts exhibited higher catalytic performance than Ni/Al2O3 and the commercial reference Meth® 134 (T = 200–300 °C, P = 5 bar·g). This increase of catalytic activity is attributed to the higher amount of CO2 adsorbed on the catalyst. Among the selected promoters, La2O3 showed the highest catalytic activity (XCO2=+20% at 300 °C) due to the enhancement of nickel reducibility, nickel dispersion and the presence of moderate basic sites. In addition, Ni-La2O3/Al2O3 was stable for one week, while the unpromoted catalyst exhibited a slight decline in its activity. Accordingly, the technical catalyst proposed in this study could be used directly in compact reactors for CO2 methanation with much higher activity than the commercial reference.

Analysis of rural economic restructuring driven by e-commerce based on the space of flows: The case of Xiaying village in central China

In recent years, China's rural areas have undergone intense restructuring motivated by various flows derived from e-commerce, which has triggered a new wave of rural rejuvenation. Attempting to reveal the process and mechanism of rural economic restructuring driven by e-commerce, this paper takes Xiaying village in central China to conduct an empirical study by introducing the theory of “space of flows” and applying the method of semi-structured interview. The results show that e-commerce has become a technical catalyst to the variation of industry structure, employment pattern and household economy. Xiaying village has performed a leap from traditional agriculture to commercial service and constructed a complete e-commerce oriented industry chain, which is distinguished from the traditional path of rural modernization adhering to the gradual evolution of the primary, secondary and tertiary industry in China. In response, the employment pattern is diversified and tends to be de-agriculturalization, thus providing an economic advancement opportunity for rural households. As a matter of fact, rural elites, technology innovation (e-commerce platform), resource endowments and government support all contributed greatly to this restructuring process. What distinguishes it from others is the strong mobility and exchange of urban and rural elements, which functions as the initial engine. Essentially, this transition can be considered as the impact of the network on the geographic space restructuring rural economy.

Revealing Catalytically Relevant Surface Species by Kinetic Isotope Effect Spectroscopy: H-Bonding to Ester Carbonyl of trans-Ethyl Pyruvate Controls Enantioselectivity on a Cinchona-Modified Pt Catalyst.

Monitoring active surface species on an operating technical catalyst is a challenging task due to the presence of multiple different adsorption sites and the abundance of bulk species. In this work, kinetic isotope effect (KIE) spectroscopy is introduced to capture the signals of catalytically relevant hydrogenation species from the IR spectroscopic detection in attenuated total reflection mode. The catalytic interface formed between a cinchona-modified Pt/Al2O3 catalyst and the solvent toluene is sensitively probed directly at the rate limiting step(s) during the asymmetric hydrogenation of ethyl pyruvate by measuring the effects of substituting H2 by D2 kinetically and spectroscopically in the same operando experiment. The application of KIE spectroscopy provides unprecedented molecular level insight into the structure of the diastereomeric intermediate surface complex and the phenomenon rate enhancement, which revolutionizes our understanding of chirally modified metal catalysts.

Modularity research to guide MOSA implementation

The US Department of Defense’s acquisition strategy incorporates directives to encourage the use of open architectures and modular solutions through the Modular Open Systems Approach (MOSA). The ways in which open standards are currently implemented, and programmatic guidance regarding the adoption of modular approaches, are inadequate, however, because of limitations on how modularity is objectively viewed to achieve its perceived benefits. Furthermore, current examples of implementations of modular concepts largely do not consider interdependencies at the enterprise level. This paper reviews ongoing research on modularity and openness, to synthesize best practices, community driven knowledge, and technical and programmatic catalysts that can better shape the appropriate adoption of MOSA. These items will be part of a comprehensive decision-making framework that can provide guidance to program managers in defense acquisition.

Novel in Situ Techniques for Studies of Model Catalysts.

Motivated mainly by catalysis, gas-surface interaction between single crystal surfaces and molecules has been studied for decades. Most of these studies have been performed in well-controlled environments and have been instrumental for the present day understanding of catalysis, providing information on surface structures, adsorption sites, and adsorption and desorption energies relevant for catalysis. However, the approach has been criticized for being too far from a catalyst operating under industrial conditions at high temperatures and pressures. To this end, a significant amount of effort over the years has been used to develop methods to investigate catalysts at more realistic conditions under operating conditions. One result from this effort is a vivid and sometimes heated discussion concerning the active phase for the seemingly simple CO oxidation reaction over the Pt-group metals in the literature. In recent years, we have explored the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures and temperatures. In this contribution, results from catalytic CO oxidation over a Pd(100) single crystal surface using Near Ambient Pressure X-ray Photo emission Spectroscopy (NAPXPS), Planar Laser-Induced Fluorescence (PLIF), and High Energy Surface X-ray Diffraction (HESXRD) are presented, and the strengths and weaknesses of the experimental techniques are discussed. Armed with structural knowledge from ultrahigh vacuum experiments, the presence of adsorbed molecules and gas-phase induced surface structures can be identified and related to changes in the reactivity or to reaction induced gas-flow limitations. In particular, the application of PLIF to catalysis allows one to visualize how the catalyst itself changes the gas composition close to the model catalyst surface upon ignition, and relate this to the observed surface structures. The effect obscures a straightforward relation between the active phase and the activity, since in the case of CO oxidation, the gas-phase close to the model catalyst surface is shown to be significantly more oxidizing than far away from the catalyst. We show that surface structural knowledge from UHV experiments and the composition of the gas phase close to the catalyst surface are crucial to understand structure-function relationships at semirealistic conditions. In the particular case of Pd, we argue that the surface structure of the PdO(101) has a significant influence on the activity, due to the presence of Coordinatively Unsaturated Sites (CUS) Pd atoms, similar to undercoordinated Ru and Ir atoms found for RuO2(110) and IrO2(110), respectively.

Ceria-based model catalysts: fundamental studies on the importance of the metal-ceria interface in CO oxidation, the water-gas shift, CO2 hydrogenation, and methane and alcohol reforming.

Model metal/ceria and ceria/metal catalysts have been shown to be excellent systems for studying fundamental phenomena linked to the operation of technical catalysts. In the last fifteen years, many combinations of well-defined systems involving different kinds of metals and ceria have been prepared and characterized using the modern techniques of surface science. So far most of the catalytic studies have been centered on a few reactions: CO oxidation, the hydrogenation of CO2, and the production of hydrogen through the water-gas shift reaction and the reforming of methane or alcohols. Using model catalysts it has been possible to examine in detail correlations between the structural, electronic and catalytic properties of ceria-metal interfaces. In situ techniques (X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, infrared spectroscopy, scanning tunneling microscopy) have been combined to study the morphological changes under reaction conditions and investigate the evolution of active phases involved in the cleavage of C-O, C-H and C-C bonds. Several studies with model ceria catalysts have shown the importance of strong metal-support interactions. In general, a substantial body of knowledge has been acquired and concepts have been developed for a more rational approach to the design of novel technical catalysts containing ceria.