Catalyst Poisoning Research Articles

In-Situ Spectroscopic Investigation of 3-D Gas Diffusion Electrodes for Fuel Cell Reactions in Half-Cell Setups

Significant work has already been done in understanding proton exchange membrane fuel cells (PEMFC) over the past decades. In-situ visualization of the fuel-cell reactions has developed considerably and has also helped in understanding the challenges which still exist in various steps of electrochemical processing. Gas diffusion electrode half-cells have been widely promoted for fundamental catalysis research and when coupled with techniques like X-ray absorption spectroscopy (XAS) can be used for in-situ/operando studies of the reaction mechanisms in fuel cell reactions. This is particularly important to address the challenges in low temperature PEMFCs (eg. degradation of catalyst during durability tests) as well as high temperature PEMFCs (eg. poisoning of the Pt catalyst and low oxygen solubility in phosphoric acid).In this presentation, an effort will be made to illuminate the catalytic characteristics during oxygen reduction reaction using in-situ XAS. The co-adsorption of H3PO3 and CO on platinum catalysts will be investigated using the Δµ XANES technique by following the signatures of different species adsorbed on the catalyst surface, and the Efix technique which follows the variation of signal intensity at a fixed energy near to the white line to follow the changes in Pt oxidation. During CO removal through cyclic voltammetry in the presence of 800 µM H3PO3 (as shown in the figure provided) it is possible to see a clear change in signal intensity around the potential of 250 mVAg/AgCl, which was associated with the oxidation of H3PO3 to H3PO4, since CO oxidation takes place at higher potentials (above 600 mVAg/AgCl). It is also interesting to note that when oxidizing H3PO3 to H3PO4, the platinum surface significantly reduced. With these experiments, it can be concluded that the Efix technique has a great potential to better understand what happens to Pt during the oxidation of H3PO3, as well as to identify more clearly the oxidation potential of this species, which is not easy to do based on the electrochemical data alone. Considering that this species is one of the main species responsible for the poisoning of the Pt catalyst during the operation of fuel cells, it is extremely important to understand the life cycle of this compound so that the operating conditions can be adapted to maximize the performance of the catalyst and develop new catalysts more resistant to poisoning by phosphorous species for HT-PEMFCs.Acknowledgements:Prof. Matthias Arenz from University of Bern, Martin Prokopand Tomàs Bystrom from University of Chemistry and Technology Prague, Michael Haumann, Freie Universität Berlin are gratefully thanked for their collaboration. German Research Foundation DFG Project ID RO 2454/19-1, the Bavarian Gender Equality Grant 2019-2021 (for Women in Academia), Petra III DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, P65 beamline (I-20211432) and KMC-3 beamline BESSY (Berlin,Germany). Figure 1

Controlling Selectivity in Electrocatalysis By Ionic Liquids: Oxidation of 2,3-Butanediol on Pt(hkl) Electrodes Modified By [C2C1im][Otf

In heterogeneous catalysis, ionic liquids (ILs) are used as chemical modifiers to control selectivity. In our work, we aim to apply the same concept to electrocatalytic systems.As a model reaction, we studied the electrooxidation of 2,3-butanediol on the low-index Pt(111), Pt(100) and Pt(110) surfaces in an acidic environment. We modified the surfaces with the IL 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C2C1Im][OTf]) dissolved in the aqueous electrolyte. The reaction mechanisms on the different surfaces were studied by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS) in combination with density functional theory (DFT).The oxidation of 2,3-butanediol is highly structure dependent. On Pt(111), the oxidation occurs in two steps, forming acetoin as an intermediate and diacetyl as the final product. On Pt(110), only the first oxidation step takes place, forming acetoin as the final product. No adsorbed COads is formed during the reaction on either surface. On Pt(100), the final product is acetoin. However, adsorbed COads is formed, which acts as a catalyst poison. On Pt(111), already low concentrations of IL (0.001 M) shift the selectivity towards acetoin from 19% to 56%.[1] We propose that the potential dependent co-adsorption of the [OTf]- anion suppresses the adsorption of OH species required for oxidation in the potential region of the second oxidation step. On the Pt(100) surface, IL suppresses the formation of poisoning COads while the surface remains active for the target reaction.[2] Our results demonstrate the potential of ILs to control selectivity in electrocatalytic reactions.[1] T. Yang, J. Yang, X. Deng, E. Franz, L. Fromm, N. Taccardi, Z. Liu, A. Görling, P. Wasserscheid, O. Brummel, J. Libuda, Angewandte Chemie International Edition 2022, 61, e202202957.[2] J. Yang, E. Franz, L. Fromm, N. Taccardi, A. Görling, P. Wasserscheid, O. Brummel, J. Libuda, in preparation.

Degradation Processes in Bipolar Membrane CO2-Electrolysis Studied by Time-Resolved X-Ray Tomography

Electrochemical reduction of carbon dioxide via CO2 co-electrolysis (CO2ELY) is an essential process to produce non-fossil chemical feedstock acting as CO2 sink. The required electrical energy can be harvested from temporal surplus of renewable energy sources like solar or wind. Employing a bipolar electrolyte membrane (BPM) in forward-bias is a promising approach to mitigate fundamental problems of the current technological fore-runner design that employs an anion exchange membrane (AEM). We employed synchrotron time-resolved X-ray tomographic microscopy (XTM) to study degradation processes in BPM CO2ELY.In forward-bias BPM co-electrolysis, the cation exchange layer (CEL) faces the anode to provide favorable acidic conditions for the oxygen evolution reaction. Such acidic anode allows using pure water as electrolyte eliminating the salt precipitation at the cathode observed for AEM CO2ELY. As the second major issue in AEM CO2ELY, (bi)carbonate ions formed at the cathode are transported to the anode presenting a major obstacle for high CO2 conversion efficiency. The then required effort to separate CO2 from the electrolyte further reduces the overall energy efficiency. Employing a BPM and introducing the CEL prevents (bi)carbonate ions reaching the anode. BPM CO2ELY retains at the same time the advantages of AEM CO2ELY of performing CO2 reduction under alkaline conditions with the anion exchange layer (AEL) of the BPM facing the cathode.However, BPM CO2ELY suffers from low current density and poor stability in the range of only a few hours. Current limiting factors and degradation processes as well as the affected components are rarely investigated and poorly understood. Processes that have been brought forward are cathode flooding similar to fuel cells or catalyst poisoning. We employ synchrotron XTM to investigate structural dynamics in CO2ELY during operation. The brilliant synchrotron source allows us to acquire one full high-quality scan with a voxel size of 2.75 um in 1 s. We acquired one scan every minute for one hour during electrochemical operation.The image data reveals the formation of gas bubbles at the AEL-CEL junction and ultimately delamination of the BPM. We explain the gas formation as the recombination of (bi)carbonate ions with hydrogen ions at the junction producing gaseous CO2. This CO2 additionally reaches the anode by diffusion causing partial delamination of the anode catalyst layer. CO2 escaping from the AEL surface at the anode forms high-pressure gas bubbles that break the water wet catalyst layer. A diffusive model considering the transport of ions and neutral CO2 is able to capture the mechanism.Our imaging experiments provide insights not attainable by other diagnostic methods and highlight the need for fundamental research on forward-bias BPM CO2ELY. Knowledge based on AEM CO2ELY and fuel cells is not necessarily directly applicable and specific studies on BPM CO2ELY are required to increase performance and stability.We gratefully acknowledge provision of beamtime at TOMCAT, SLS, Paul Scherrer Insititut, Villigen PSI, Switzerland.Figure 1: Tomographic slice of CO2-electrolyser (cathode to the left) a) before operation and running water through anode b) after 23 minutes operation at 3.5V constant potential showing liquid water dynamics at cathode, membrane swelling, gas formation within the membrane and anode catalyst layer disintegration. Figure 1

SO2-Tolerant Electrocatalytic Reduction of CO2 from Simulated Industrial Flue Gas

The electrochemical reduction of CO2 using copper-based electrocatalysts offers a route to produce high-value multicarbon (C2+) products from renewable electricity (Nat. Catal. 4, 952-958 (2021); Nature 614, 262-269 (2023)). To date, the efficient electrocatalytic conversion of CO2 to multicarbon products has only been possible when using impurity-free CO2 sources, such as from direct air capture. The generation of such high-grade CO2 streams is expensive, accounting for almost half of the total energy required for both capture and electroreduction processes (Nat. Catal. 4, 952-958 (2021)). Conversely, capturing CO2 from point sources, such as industrial flue gas, is more efficient due to the higher concentration of CO2 in the feed. However, trace amounts of sulfur dioxide (10 ~ 400 ppm SO2) inherently present in these streams will significantly degrade the CO2 conversion process. All previous attempts to convert CO2 with SO2 present in the feed have resulted in immediate catalyst poisoning and an irreversible loss of CO2 conversion activity.In this study, we designed a modified catalyst layer to react a stream of dilute CO2 containing 400 ppm SO2 to multicarbon products with high stability and performance metrics that match or exceed those achieved with pure CO2 streams. Driven by density function theory and COMSOL simulations, we designed an ionomer:copper:polytetrafluoroethylene (PTFE) (ICP) electrode that features both hydrophobic and highly-charged hydrophilic domains to limit water adsorption and promote CO2 over SO2 transport near the electrochemically active sites. This deactivates the SO2 poisoning mechanism, thus enabling stable and efficient CO2 conversion (see figure). Our approach achieved a sustained C2+ Faradaic efficiency (FE) of 50% for the initial 160 hours at 100 mA cm-2.In order to improve the overall C2+ current efficiency (jC2+) towards industrial scales, we applied our strategy in high-surface-area copper electrodes. We achieved CO2 conversion in the presence of 400 ppm SO2 with a C2+ FE of 76% at a current density of 700 mA cm-2, surpassing what can be achieved in existing integrated CO2 capture-electrolysis systems that use pure CO2. Overall, our approach provides a fully 140-fold increase in performance (FEC2+ × jC2+) compared to the best prior CO2 conversion systems with added SO2 (Nat. Nanotechnol. doi: 10.1038/s41565-022-01286-y (2023); J. Am. Chem. Soc. 141, 9902-9909 (2019)). These findings represent an important advancement in the field of CO2 conversion and highlight the potential of our strategy for industrial-scale applications. Figure 1

Preventing Pt Catalysts in PEM Fuel Cells from CO Poisoning by Getting COPROX to Work

Proton-exchange membrane fuel cells still require CO-scrubbed H2 feedstreams to sustain long-duration performance. Sufficiently CO-free H2 costs an order of magnitude more than steam refining fossil fuels to generate H2—and until green processes produce the bulk of H2, preferential oxidation of CO from H2-rich feedstreams, also known as COPROX, is a necessity. We design architected catalytic platforms as ultraporous metal nanoparticle–modified oxide aerogels in which a covalently bonded oxide nanoparticulate network (NPs) supports comparably sized catalytic nanoparticles (NPs). The degree of physical and chemical interfacial intimacy stabilizes the more catalytically active low valent state of Cu and the ultraporous catalytic platform demonstrates high activity and on-stream durability for thermal catalysis of CO [1]. We then evaluate the selectivity and activity of this architected catalyst and a related aerogel, Cu/GdxCe1–xO2, for preferential oxidation of CO (COPROX) in H2 feedstreams. The catalysts convert >95% of CO at temperatures that prevent oxidation (consumption) of the H2 fuel (a purification reaction necessary to prevent poisoning of the anode catalysts in H2 fuel cells). The architected Cu/ceria catalysts achieve >95% selectivity vs. H2 and maintain this unprecedented activity for >16 h at 100°C in dry or humidified feedstreams [2,3]. The ability to purify H2 from steam-reformed fuels for use in proton-exchange membrane fuel cells increases power source flexibility as the world transitions to more sustainable, carbon-neutral routes to highly purified H2.[1] Stabilization of reduced copper on ceria aerogels for CO oxidation. C. L. Pitman, A. M. Pennington, T. H. Brintlinger, D. E. Barlow, L. F. Esparraguera, R. M. Stroud, J. J. Pietron, P. A. DeSario, D. R. Rolison, Nanoscale Adv. 2020, 2, 4547–4556 (10.1039/D0NA00594K).[2] Preferential oxidation of CO in H2-containing gas. T.G. Novak, D.R. Rolison, P.A. DeSario, US Patent Application, filed Jan 27, 2023 [Navy Case #210,945].[3] Cu/CeO2 and Cu/Gd-substituted CeO2 aerogels for active, selective, and stable COPROX catalysis. T.G. Novak, P.A. DeSario, T.H. Brintlinger, R.H. DeBlock, J.W. Long, and D.R. Rolison, ACS Sus. Chem. Eng. 2023, 11, 2853–2860 (10.1021/acssuschemeng.2c06158).

(Invited) The Stability of Nanomaterials in Electrochemical Energy Conversion, Illustrated on Selected Examples

Energy is the most valuable resource for human activity and the foundation for all human progress. Thereby, electrochemical processes are considered a crucial technology for our future society's energy landscape. Catalysts are fundamental components of these processes, and the ability to control their structure and composition during synthesis is essential for obtaining high-performance and stable catalysts while preserving critical resources. The stability of materials that can endure reaction conditions over extended periods is of immense significance. In nanoparticle systems, typical deactivation mechanisms include catalyst agglomeration, dissolution, coalescence, Ostwald ripening, support corrosion, or poisoning.[1] In this conference contribution, I will discuss the prerequisites for stable electrocatalysts using selected examples. I will demonstrate how the catalyst's environment and support material can prevent degradation based on our recent observations.[2-5][1] Y. Shao-Horn, W. C. Sheng, S. Chen, P. J. Ferreira, E. F. Holby, D. Morgan, Top. Catal., 46, 285-305, 2007, J. C. Meier, I. Katsounaros, C. Galeano, H. J. Bongard, A. A. Topalov, A. Kostka, A. Karschin, F. Schüth, K. J. J. Mayrhofer, Energy & Environmental Science 2012, 5, 9319-9330.[2] D. Göhl, H. Rueß, A. M. Mingers, K. J. J. Mayrhofer, J. M. Schneider, M. Ledendecker, J. Electrochem. Soc., 169, 011502, 2022[3] D. Göhl, A. Garg, P. Paciok, K. J. Mayrhofer, M. Heggen, Y. Shao-Horn, R. E. Dunin-Borkowski, Y. Román-Leshkov, M. Ledendecker, Nat. Mater., 19, 287-291, 2020[4] D. Göhl, H. Rueß, M. Pander, A. R. Zeradjanin, K. J. Mayrhofer, J. M. Schneider, A. Erbe, M. Ledendecker, J. Electrochem. Soc., 167, 021501, 2020[5] M. Ledendecker, S. Krick Calderón, C. Papp, H. P. Steinrück, M. Antonietti, M. Shalom, Angew. Chem. Int. Ed., 54, 12361-12365, 2015

(2022-2023 ECS Toyota Young Investigator Fellowship) Enhanced Water Electrolysis Using Layered Coaxial Nanowire Electrodes

Novel electrocatalytic approaches are urgently needed to increase the energy efficiency and decrease the cost of hydrogen production by PEM water electrolyzers. Recently, we developed a novel catalytic platform, the layered coaxial nanowire electrode (LCANE), which enables PEM water electrolyzers with higher energy efficiency and reduced usage of precious metal catalysts. Electrolyzers based on the LCANE approach use a thin film of IrO2-decorated Pt that is intimately interfaced with an ionomer membrane in the form of vertically-aligned coaxial nanowires. Each nanowire consists of a Pt shell encapsulating an ionomer core, with the Pt shell further decorated by IrO2 clusters. The top region of each nanowire bends to form a layer of in-plane aligned Pt/IrO2 nanowires, providing excellent in-plane electronic conductivity. This unique catalyst/electrode geometry offers several key advantages. By localizing ionomer within the nanowire core, the exterior surface of the catalyst remains free from ionomer, eliminating thin-film transport barriers and preventing catalyst poisoning by ionomer adsorption. The vertically aligned sections of the nanowires provide non-tortuous transport of reactants and products, with abundant pore space for facile access of water and removal of oxygen. Close integration of catalyst and ionomer provides improved proton access and eliminates stranding of catalyst. By incorporating catalyst in the form of a thin film and replacing some of the Ir with Pt, lower Ir loading (as low as 0.1 mg/cm2) is achieved without sacrificing surface area or performance.AcknowledgmentThis work was supported by the ECS-Toyota Young Investigator Fellowship and by the Laboratory Directed Research and Development program at Los Alamos National Laboratory.

Operando 3D-Monitoring of the Oxygen Partial Pressure (p(O2)) within a Polymer Electrolyte Membrane Fuel Cell (PEMFC) during Cell Operations at Higher Temperatures

Introduction:Hydrogen technologies, especially the Proton Exchange Membrane Fuel Cell (PEMFC), are promising alternative power sources, due to their low to non-carbon emission, high power density, high efficiency, and fast start-up. Despite their high potential and expected major impact on the economy of the future, there are still challenges to overcome, before PEMFCs can be globally commercialized. Soon, PEMFCs operated above 100°C are expected to be used for automobiles, due to their use of smaller and lighter radiators, higher reaction rates and lower susceptibility to catalyst poisoning. To achieve this goal however, high-temperature PEMFCs need a higher performance, stability, and durability, while reducing the cost at the same time. The performance, durability and stability of a fuel cell are related to the distribution of physical and chemical parameters, like e.g., oxygen partial pressure (p(O2)). During the operation of the fuel cell, the distribution of those parameters is inhomogeneous.[1] Therefore, we used an in-house developed 3-dimensional non-destructive real-time/space visualization system to achieve an understanding of the p(O2) inside the fuel cell during operation at higher temperatures.Experimental:The PEMFC used for this experiment has an active area of 4 cm2 and uses 10 straight gas flow channels. Prior to the assembling, 5 pinholes with a diameter of 90 µm were manufactured into the GDL on the cathode side both underneath the rib and the gas flow channel (Fig. 1). Those pinholes are also manufactured into the current collector and insulator of the PEMFC on cathode side. The holes are used to insert optical fibers from outside the cell to approximately 20 µm (adjustable with an accuracy of 1 µm) above the catalyst layer of the CCM. Prior to the use, the fibers with a core diameter of 10 µm are etched in HF solution to reduce their clad diameter from 125 to 50 µm. Furthermore, the apex of the fiber is cleaved perpendicular to the axis of the fiber. Before insertion an oxygen sensitive dye (PtTFPP, (Fig. 2)) is applied to the apex of the fibers. PtTFPP has absorption peaks at 407, 530 and 540 nm and an emission peak at 650 nm. The emission peak is quenched by oxygen partial pressure, and the emission intensity decreases monotonically with increasing oxygen partial pressure. For the excitation, a laser with a wavelength of 532 nm is used and the emitted light is captured by a CCD camera.[2] Visualizations were carried out at 80, 90, 100, 110 and 120 oC at a constant water vapor pressure of 37.97 kPa, which equals 80, 53.6, 36.8, 25,9 and 18.5% RH respectively, at increasing current densities. Prior to the visualization, calibrations, and performance tests in form of IV and CV were carried out for each temperature. The gas flow rate during the experiments was set to 100 mL/min Air/H2 (parallel flow) at cathode and anode respectively. Results and Discussion:The IV performance tests showed decreasing cell performance with increasing temperatures, which was expected because of the increasing resistance due to drying out of the membrane. Furthermore, a decrease of the ECSA was observed with increasing temperatures, which could also be due to the drying out of the membrane as well as the binding material around the catalyst nanoparticles which reduces gas diffusion and the effective catalyst surface area. In this first try, the monitoring was done with 3 fibers under one rib located near the inlet, the middle of the cell and near the outlet of the cell. With increasing current density, the oxygen partial pressure was decreasing at every temperature. Interestingly, the oxygen partial pressure distribution changed with increasing temperature. The reason for the changing oxygen partial pressure distribution could be due to accumulation of heat (Fig. 3) and increasing water vapor pressure at higher temperatures. Further experiments with 5 fibers including measurements in the gas flow channel as well as measurements with back pressure to increase the cell performance will be done shortly to confirm this finding.[1] Y. Kakizawa, C. L. Schreiber, S. Takamuku, M. Uchida, A. Iiyama, J. Inukai, Visualization of the oxygen partial pressure in a proton exchange membrane fuel cell during cell operation with low oxygen concentrations, J. Power Sources, 483, 229193 (2021).[2] Y. Kakizawa, T. Kobayashi, M. Uchida, T. Ohno, T. Suga, M. Teranishi, M. Yoneda, T. Saiki, H. Nishide, M. Watanabe, A. Iiyama, J. Inukai, Oscillation mechanism in polymer electrolyte membrane fuel cell studied by operando monitoring of oxygen partial pressure using optical probes, J. Surf. Finish. Soc. Jpn, 72, 230 (2021). Figure 1

Palladium Catalysts for Methane Oxidation: Old Materials, New Challenges.

ConspectusMethane complete oxidation is an important reaction that is part of the general scheme used for removing pollutants contained in emissions from internal combustion engines and, more generally, combustion processes. It has also recently attracted interest as an option for the removal of atmospheric methane in the context of negative emission technologies. Methane, a powerful greenhouse gas, can be converted to carbon dioxide and water via its complete oxidation. Despite burning methane being facile because the combustion sustains its complete oxidation after ignition, methane strong C-H bonds require a catalyst to perform the oxidation at low temperatures and in the absence of a flame so as to avoid the formation of nitrogen oxides, such as those produced in flares. This process allows methane removal to be obtained under conditions that usually lead to higher emissions, such as under cold start conditions in the case of internal combustion engines. Among several options that include homo- and heterogeneous catalysts, supported palladium-based catalysts are the most active heterogeneous systems for this reaction. Finely divided palladium can activate C-H bonds at temperatures as low as 150 °C, although complete conversion is usually not reached until 400-500 °C in practical applications. Major goals are to achieve catalytic methane oxidation at as low as possible temperature and to utilize this expensive metal more efficiently.Compared to any other transition metal, palladium and its oxides are orders of magnitude more reactive for methane oxidation in the absence of water. During the last few decades, much research has been devoted to unveiling the origin of the high activity of supported palladium catalysts, their active phase, the effect of support, promoters, and defects, and the effect of reaction conditions with the goal of further improving their reactivity. There is an overall agreement in trends, yet there are noticeable differences in some details of the catalytic performance of palladium, including the active phase under reaction conditions and the reasons for catalyst deactivation and poisoning. In this Account we summarize our work in this space using well-defined catalysts, especially model palladium surfaces and those prepared using colloidal nanocrystals as precursors, and spectroscopic tools to unveil important details about the chemistry of supported palladium catalysts. We describe advanced techniques aimed at elucidating the role of several parameters in the performance of palladium catalysts for methane oxidation as well as in engineering catalysts through advancing fundamental understanding and synthesis methods. We report the state of research on active phases and sites, then move to the role of supports and promoters, and finally discuss stability in catalytic performance and the role of water in the palladium active phase. Overall, we want to emphasize the importance of a fundamental understanding in designing and realizing active and stable palladium-based catalysts for methane oxidation as an example for a variety of energy and environmental applications of nanomaterials in catalysis.

Biodiesel production via transesterification reaction

Global warming, climate change, local air pollution, ozone depletion, acid rain and depletion of fossil fuel are the major global environmental issues. Presently, non-renewable fossil fuels meet up to 80% of the world’s energy demand. Rapid consumption of fossil fuels as well as rising environmental pollution caused by extreme CO2 emissions, sulphur dioxide, and aromatic hydrocarbons has become crucial in searching for a clean and renewable energy source such as biodiesel. With continuous growth in the world’s population, rapid industrialization, urbanization, and economic growth, fossil fuel consumption is escalating to meet the global energy demand. Biodiesel is renewable, non-toxic, environment-friendly and an economically feasible options to tackle the depleting fossil fuels and its negative environmental impact. Biodiesel is an alternative fuel made by transesterification reaction of oil and alcohol under the influence of catalyst. Biodiesel is an alcoholic ester of various fatty acids, also known as FAME (Fatty Acid Methyl Esters). In the process of transesterification, the performance of the catalyst is the key factor of the biodiesel yield. Catalysts used in biodiesel production are classified as homogeneous, heterogeneous, and enzymatic catalysts. The incorporation of a catalysis-based transesterification reaction generally increases the rate of reaction and enhances the yield of the end product. In case of homogeneous catalysts, there are problems of catalyst poisoning and contamination. Heterogeneous acid catalysis has a lesser toxic effect and gives rise to fewer environmental problems compared to the homogeneous mode. The cost of each specific catalyst depends on various factors, including the source, synthesis method, and its reusability. Generally, using waste or biomass as sources of catalysts may reduce the price of commercially available solid catalysts.

Nickel-Catalyzed Enantioselective Hydrothiocarbonylation of Cyclopropenes.

Hydrothiocarbonylation of olefins using carbon monoxide and thiols is a powerful method to synthesize thioesters from simple building blocks. Owing to the intrinsic challenges of catalyst poisoning, transition-metal-catalyzed asymmetric thiocarbonylation, particularly when utilizing earth abundant metals, remains rare in the literature. Herein, we report a nickel-catalyzed enantioselective hydrothiocarbonylation of cyclopropenes for the synthesis of a diverse collection of functionalized thioesters in good to excellent yields with high stereoselectivity. This new method employs an inexpensive, air-stable nickel(II) precursor, which provides enhanced catalyst fidelity against CO poisoning compared to nickel(0) catalysts.

Direct C−C Double Bond Cleavage of Alkenes Enabled by Highly Dispersed Cobalt Catalyst and Hydroxylamine

AbstractThe utilization of a single‐atom catalyst to break C−C bonds merges the merits of homogeneous and heterogeneous catalysis and presents an intriguing pathway for obtaining high‐value‐added products. Herein, a mild, selective, and sustainable oxidative cleavage of alkene to form oxime ether or nitrile was achieved by using atomically dispersed cobalt catalyst and hydroxylamine. Diversified substrate patterns, including symmetrical and unsymmetrical alkenes, di‐ and tri‐substituted alkenes, and late‐stage functionalization of complex alkenes were demonstrated. The reaction was successfully scaled up and demonstrated good performance in recycling experiments. The hot filtration test, catalyst poisoning and radical scavenger experiment, time kinetics, and studies on the reaction intermediate collectively pointed to a radical mechanism with cobalt/acid/O2 promoted C−C bond cleavage as the key step.

Efficient removal of Hg0 by the combination of CuO and excellent carrier Ta2O5

A carrier Ta2O5 was introduced and combined with CuO for the removal of Hg0 in flue gas This combination exhibited an excellent performance and demonstrated robust resistance to both water and SO2 when compared to commonly used carriers (TiO2, Al2O3, etc.). CuO0.35/Ta2O5 manifested the highest Hg0 removal efficiency and excellent stability among all synthesized samples, reaching nearly 95 % in the initial stage. The introduction of O2 can improve the removal rate of Hg0, and the present of SO2 did not lead to catalyst poisoning. Physicochemical characterization revealed that CuO0.35/Ta2O5 possessed a high specific surface area and good thermal stability. Besides, copper was evenly distributed on the catalyst surface, and the combination of CuO and Ta2O5 enhanced the oxidation property of the catalyst. The removal mechanism of Hg0 was investigated and it was found that Hg0 binded to lattice oxygen on the catalyst after oxidation. A portion of the bound mercury was adsorbed on the catalyst, while the remainder was released into the flue gas.

Central composite design approach for concurrent desulfurization and denitrogenation of model liquid fuel over Mo‐AAC

AbstractThe primary objective of this work was to investigate the simultaneous removal of refractory sulfur (dibenzothiophene, DBT) and nitrogen compounds (indole, IND) from model gasoline. This research aimed to develop an efficient adsorption process to mitigate the emission of sulfur oxide and nitrogen oxides, which pose direct threats to human health and the environment. Additionally, the study focused on addressing technical challenges encountered in the refinery process, particularly the poisoning of catalysts due to the presence of these compounds. To achieve the study's goals, granular activated carbon (GAC) was subjected to acid treatment for modification. Molybdenum species were then incorporated into the acid‐treated GAC using the wet impregnation technique. The composition and distribution of elements on the surface of the modified GAC (Mo‐AAC) were analyzed via X‐ray photoelectron spectroscopy (XPS). Various characterization techniques were employed to confirm the uniform dispersion of molybdenum species on the GAC surface. The specific surface area of the adsorbent was increased from 257 m2/g to 316 m2/g following the acid treatment and molybdenum modification. The study explored the impact of several key parameters on the removal of DBT and IND using central composite design (CCD). A regression model was derived using CCD through hybrid central composite design, and its adequacy was verified with the means of tests such as analysis of variance (ANOVA), a lack of fit test, and residuals distribution consideration. Experimental results match well with the results obtained by CCD model, justifying the accuracy of models. The results showed that all four parameters have a significant impact on removal of DBT and IND. Increasing temperature and the adsorbent dose positively affected the removal of both DBT and IND, indicating that higher temperatures and greater adsorbent dosages improved removal efficiency. On the other hand, the concentration of DBT and IND had a negative impact, signifying that higher initial contaminant concentrations hindered removal efficiency. The study determined the optimum initial contaminant concentrations for DBT and IND, temperature, and adsorbent dose to be 186 mg/L, 50 mg/L, 25.5°C, and 32 g/L, respectively. These conditions yielded the highest removal efficiency. The research demonstrated that Mo‐AAC has the capability to effectively reduce the sulfur and nitrogen content of model gasoline, making it a promising solution for addressing environmental and refinery challenges associated with these compounds.

Recent Advances in Nickel Catalyzed Carbonylative Reactionsviathe Insertion of Carbon Monoxide†

Comprehensive SummaryCarbonyl compounds have attracted considerable attention due to their extensive applications in drug discovery. Furthermore, they are important synthetic intermediates for the construction of carbon‐carbon and carbon‐heteroatom bonds. Transition‐metal‐catalyzed carbonylation via the insertion of CO is one of the most efficient and straightforward strategies to access carbonyl compounds. However, most of the transition‐metal‐catalyzed carbonylative reactions require expensive and toxic noble‐metal catalysts. Therefore, there is a growing demand for the exploration of nickel‐catalyzed carbonylative reactions via the insertion of CO due to the earth abundance and low cost of nickel. Compared with the well‐established palladium‐catalyzed carbonylative reactions, nickel‐catalyzed analogous transformations have been relatively underdeveloped. This is primarily because CO strongly binds to nickel, often resulting in catalyst poisoning. In recent years, some research groups have focused on using CO surrogates or NN2pincer nickel catalyst to circumvent the formation of Ni(CO)4. Nickel‐catalyzed carbonylation has been applied in the construction of carbonyl‐containing compounds, such as ketones, carboxylic acids, thioesters, acyl chloride and carboxamides.

Enhancing Hydrogen Production from the Photoreforming of Lignin.

Photoreforming of lignocellulose biomass is widely recognised as a challenging but key technology for producing value-added chemicals and renewable hydrogen (H2 ). In this study, H2 production from photoreforming of organosolv lignin in a neutral aqueous solution was studied over a 0.1 wt % Pt/TiO2 (P25) catalyst with ultraviolet A (UVA) light. The H2 production from the system employing the lignin (~4.8 μmol gcat -1 h-1 ) was comparable to that using hydroxylated/methoxylated aromatic model compounds (i. e., guaiacol and phenol, 4.8-6.6 μmol gcat -1 h-1 ), being significantly lower than that from photoreforming of cellulose (~62.8 μmol gcat -1 h-1 ). Photoreforming of phenol and reaction intermediates catechol, hydroquinone and benzoquinone were studied to probe the mechanism of phenol oxidation under anaerobic photoreforming conditions with strong adsorption and electron transfer reactions lowering H2 production from the intermediates relative to that from phenol. The issues associated with catalyst poisoning and low photoreforming activity of lignins demonstrated in this paper have been mitigated by implementing a process by which the catalyst was cycled through anaerobic and aerobic conditions. This strategy enabled the periodic regeneration of the photocatalyst resulting in a threefold enhancement in H2 production from the photoreforming of lignin.

A New Ammonia Kinetic Model in Ru-Catalyzed Steam-Reforming Reaction Containing N2 in Natural Gas

Hydrogen for building fuel cells is primarily produced by natural-gas steam-reforming reactions. Pipeline-transported natural gas in Europe and North America used to contain about 1% to 5% N2, which reacts with H2 in steam-reforming reactions to form NH3. In the case of Ru, one of the catalysts used in natural-gas steam-reforming reactions, the activity of the NH3-formation reaction is higher than that of Ni and Rh catalysts. Reforming gas containing NH3 is known to poison Pt catalysts in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) and also poison catalysts in preferential oxidation (PROX). In this study, Langmuir–Hinshelwood-based models of the NH3-formation reaction considering H2 and CO were proposed and compared with a simplified form of the Temkin–Pyzhev model for NH3-formation rate. The kinetic parameters of each model were optimized by performing multi-objective function optimization on the experimental results using a tube-type reactor and the numerical results of a plug-flow one-dimension simple SR (steam-reforming) reactor.

Transition-Metal-Catalyzed Addition of Organosulfur Compounds to Alkynes and Alkenes: Catalysis and Catalyst Poisons.

The addition of heteroatom compounds to alkynes and alkenes is an atom-efficient method of carbon-heteroatom bond formation and is widely used as a fundamental synthetic method for the construction of functional molecules. Nevertheless, examples of transition-metal-catalyzed addition reactions of group 16 heteroatom compounds to carbon-carbon unsaturated bonds have been limited due to the widespread belief that organic sulfur and selenium compounds are representative catalyst poisons. In recent decades, however, several seminal catalytic reactions of sulfur compounds have been developed, providing important insights into catalysis and poisons. Therefore, in this paper, we focus on the transition-metal-catalyzed addition of organosulfur compounds to alkynes and alkenes, gain comprehensive insights into the catalysis and catalyst poisons, and propose concepts for the development of transition-metal-catalyzed reactions of group 16 heteroatom compounds.

Direct Visualization of CO Interaction on Oxygen Poisoned Co(0001).

The poisoning of catalysts has always been a vital issue in catalytic reactions. In this study, direct observation of the interaction of CO and oxygen-poisoned Co(0001) has been achieved with scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), and density functional theory calculation. A two-stage adsorption process of CO on a well-prepared p(2×2)-O layer covered Co(0001) was directly visualized. With increasing annealing time at a certain temperature after the CO dosage, the ordered (2 × 2) pattern formed in the first stage can be recovered, suggesting the weak interaction of CO with the O-covered Co(0001) surface in the latter stage. Compared to the clean Co(0001) surface, on an oxygen-poisoned surface, no further reaction was observed, illustrating the poisoning of the catalyst. Moreover, TPD results are in good agreement with the STM observation; a desorption energy of 0.35 eV is evaluated with a simple but accurate scheme.

Synergistic engineering of heteronuclear Ni-Ag dual-atom catalysts for high-efficiency CO2 electroreduction with nearly 100% CO selectivity

Single-atom catalysts (SACs) have emerged as attractive materials for the electrocatalytic carbon dioxide reduction (ECO2R). Dual-atom catalysts (DACs), an extension of SACs, exhibit more compelling functionalities due to the synergistic effects between adjacent metal atoms. However, the rational design, clear coordination mode, and in-depth understanding of heteronuclear dual-atom synergistic mechanisms remain elusive. Herein, a heteronuclear Ni-Ag dual-atom catalyst loaded on defective nitrogen-rich porous carbon, denoted as Ni-Ag/PC-N, was synthesized using cascade pyrolysis. The configuration of Ni-Ag dual-atom sites is confirmed as N3-Ni-Ag-N3. Ni-Ag/PC-N demonstrates a remarkable CO Faradaic efficiency (FECO) exceeding 90% over a broad range of applied potentials, i.e., from −0.7 to −1.3 V versus reversible hydrogen electrode (RHE). The peak FECO of 99.2% is observed at −0.8 V (vs. RHE). Tafel analysis reveals that the rate-determining step of ECO2R-to-CO is the formation of the *COOH intermediate, and Ni-Ag/PC-N exhibits optimal electrokinetics. In situ FTIR and in situ Raman spectra indicate accelerated production of *COOH intermediates during the ECO2R-to-CO process. Density functional theory (DFT) calculations demonstrate that the coordinated Ni atom lowers the energy barrier of *COOH intermediates formation over the Ni-Ag/PC-N surface, while the adjacent Ag atom mitigates the catalyst poisoning caused by the strong *CO affinity on the Ni atomic site.