Catalysis Research Research Articles

On the Meaning and Origins of Lignin Recalcitrance: A Critical Analysis of the Catalytic Upgrading of Lignins Obtained from Mechanocatalytic Biorefining and Organosolv Pulping

AbstractIn the broad context of catalysis for lignin valorization, the term “recalcitrance” is often used to describe the resistance of lignin to undergo chemical transformations (generally, reductive processes) rendering small molecules soluble in the reaction medium. Unfortunately, the current usage of the term “recalcitrance” often remains vague in meaning, hindering the search for better catalysts for lignin valorization. In the quest to address the research question—What is lignin recalcitrance?—we present our search for the factors responsible for the resistance of lignin to reductive catalytic processes, from various perspectives. In this study, lignins isolated as a precipitate obtained from the saccharification of water‐soluble lignocelluloses (produced by solvent‐free mechanocatalytic depolymerization of beechwood, pinewood, or sugarcane bagasse) and their counterparts isolated by solvent extraction (organosolv pulping) are investigated. The critical analysis of structure and bonding, in addition to the in‐depth understanding of results from the catalytic upgrading of lignin streams, in the presence of Raney Ni and H2 pressure under mild and extreme conditions, reveals that the simple evaluation of the total yield of liquid products provides no quantitative measure of the lignin recalcitrance. Our results shed light on the real meaning, origins and implications of “lignin recalcitrance” for catalysis research. The results demonstrate that lignin recalcitrance is associated not only with its intrinsic properties (i.e. molecular weight, the occurrence of native linkages, and their bond dissociation enthalpies) but also with its extrinsic properties (e.g. residual polysaccharides and solubility). Overall, this study presents a detailed evaluation of recalcitrance of lignin through the critical analysis of the product mixture properties (e.g. H/C and O/C ratios, molecular weight distribution, yield of key individual products, and several others).

Wüstite-based catalyst for ammonia synthesis: Structure, property and performance

Fused iron catalyst is an active and classical catalyst both for ammonia synthesis and Fischer-Tropsch synthesis which are two typical industrial processes. As it is of significance to catalysis science as well as its importance to industry, fused iron catalyst is an ideal model system for heterogeneous catalysis research. However, the precursors of fused iron catalysts were confined to Fe3O4 in the most studies. The discovery of wüstite (Fe1-xO) based catalyst is a key innovation for fused iron catalyst which necessitates the further research to obtain deeper insight into this novel catalyst.This paper summarized three major scientific issues involved in the development of wüstite based catalyst, namely, the physicochemical properties, characteristics of wüstite, as well as the mechanism leading to the high activity. Based on this novel catalyst, new concepts and opinions were proposed, and the insights and principles obtained are as follow. Hump like activity trend of reduced catalyst was first obtained with varying of Fe2+/Fe3+ in the catalyst precursor. Molecular ratio of iron oxides, single phase theory and structure of active sites were suggested to elucidate the high activity of wüstite based catalyst. In addition, new concepts and opinions such as the disproportionation of metastable wüstite and its inhibition, matching of promoters with the structural characteristics of wüstite, synergy between acidic site and basic site on the surface of catalyst, role of Al2O3 in the re-structuring of catalyst surface, mechanism of competitive reduction, strong H2 adsorption, active sites, micro-structure of α-Fe and the essence of high activity were proposed to bring light to the structure-activity relationship forming the theory system with single phase theory as the kernel of wüstite catalyst. These regularities and the theory system significantly promoted and enriched the scientific knowledge of fused iron catalyst. It is unexpected that a knowledge based improvement of a catalyst would have a strong effect on other fields of catalysis research.

Organometallics—A Foundation for Catalysis Research

ADVERTISEMENT RETURN TO ISSUEEditor's PageNEXTOrganometallics—A Foundation for Catalysis ResearchLaurel L. SchaferView Author Information Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1Cite this: Organometallics 2017, 36, 11, 2053Publication Date (Web):June 12, 2017Publication History Published online12 June 2017Published inissue 12 June 2017https://doi.org/10.1021/acs.organomet.7b00390Copyright © 2017 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1216Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (151 KB) Get e-AlertsSUBJECTS:Catalysis,Metals,Organometallic chemistry,Organometallic reactions,Reactivity Get e-Alerts

Edge‐hydroxylated Boron Nitride for Oxidative Dehydrogenation of Propane to Propylene

AbstractThe front cover artwork for Issue 10/2017 is provided by the Advanced Energy Materials and Catalysis Research Group, Dalian University of Technology and the Institute of High Energy Physics, Chinese Academy of Sciences. The image shows that a metal‐free catalyst, edge hydroxylated boron nitride, can efficiently catalyze the oxidative dehydrogenation of propane to propylene with superior selectivity and negligible CO2 emission. See the Full Paper itself at https://doi.org/10.1002/cctc.201700004.

State-of-the-art Nanofabrication in Catalysis.

We present recent developments in top-down nanofabrication that have found application in catalysis research. To unravel the complexity of catalytic systems, the design and use of models with control of size, morphology, shape and inter-particle distances is a necessity. The study of well-defined and ordered nanoparticles on a support contributes to the understanding of complex phenomena that govern reactions in heterogeneous and electro-catalysis. We review the strengths and limitations of different nanolithography methods such as electron beam lithography (EBL), photolithography, extreme ultraviolet (EUV) lithography and colloidal lithography for the creation of such highly tunable catalytic model systems and their applications in catalysis. Innovative strategies have enabled particle sizes reaching dimensions below 10 nm. It is now possible to create pairs of particles with distance controlled with an extremely high precision in the order of one nanometer. We discuss our approach to study these model systems at the single-particle level using X-ray absorption spectroscopy and show new ways to fabricate arrays of single nanoparticles or nanoparticles in pairs over a large area using EBL and EUV-achromatic Talbot lithography. These advancements have provided new insights into the active sites in metal catalysts and enhanced the understanding of the role of inter-particle interactions and catalyst supports, such as in the phenomenon of hydrogen spillover. We present a perspective on future directions for employing top-down nanofabrication in heterogeneous and electrocatalysis. The rapid development in nanofabrication and characterization methods will continue to have an impact on understanding of complex catalytic processes.

Non-Colloidal Nanocatalysts Fabricated Using Arc Plasma Deposition and Their Application in Heterogenous Catalysis and Photocatalysis

To understand technologically complex catalytic systems and to tailor both activity and selectivity in heterogeneous catalysis and photocatalysis, there is the challenge of bridging the materials gap that exists between two- and three-dimensional model catalytic systems and real catalysts, which are comprised of highly dispersed, oxide-supported metal nanoparticles. While colloid nanoparticles synthesized using wet chemistry have the potential for tuning size, shape, and composition, there are complexities related to the organic capping layers. Therefore, the development of new model catalysts without a capping layer is crucial. Coaxial vacuum arc plasma deposition (APD) is a method to fabricate non-colloidal nanocatalysts that has the potential for large-scale synthesis of nanocatalysts and, at the same time, allows for systematic investigation of intrinsic factors that affect catalytic activity. In this article, we describe the fabrication of catalytic nanoparticles using APD, and their application in heterogeneous catalysis and photocatalysis research. Direct vaporization of metallic materials to deposit active materials on two-dimensional or three-dimensional oxide supports has drawn considerable interest due to its simplicity, high reproducibility, and the possibility for large-scale production. We highlight recent studies on metal–support interactions, the effect of doping on the oxide, and hot electron-driven chemical reactions. In the case of photocatalysis, APD was used to fabricate metal nanoparticles on a hierarchically porous oxide; enhanced hydrogen evolution by doping and porosity was also demonstrated. Therefore, the materials gap in catalysis can be bridged by the potential for large-scale synthesis of a variety of catalysts using APD.

Magnetic Fe3O4 nanoparticles supported amine: a new, sustainable and environmentally benign catalyst for condensation reactions

Diethylenetriamine immobilized on magnetic Fe3O4 nanoparticles (DETA-Fe3O4) was successfully prepared as a new and well dispersed magnetically separable amine catalyst. The structure of the resulting catalyst was well characterized by a series of analysis techniques such as FT-IR, SEM, EDX, VSM, TGA and XRD. The catalytic activity of DETA-Fe3O4 was evaluated with Knoevenagel condensation of active methylene compounds with aromatic aldehydes. Interestingly, the cyclocondensation of anthranilamide and aldehydes were effectively catalyzed by DETA-Fe3O4 in water, and the desired products (2,3-dihydroquinazoline-4(1H)-ones) were afforded in admirable yields. Catalysis research under aqueous medium (water) also makes this synthetic protocol ideal and fascinating from the environmental point of view. The amine catalyst can be magnetically recovered after the reaction and can be reused many times without appreciable decrease in activity.

The Degree of Rate Control: A Powerful Tool for Catalysis Research

The “degree of rate control” (DRC) is a mathematical approach for analyzing multistep reaction mechanisms that has proven very useful in catalysis research. It identifies the “rate-controlling transition states and intermediates” (i.e., those whose DRCs are large in magnitude). Even in mechanisms with over 30 intermediates and transition states, these are generally just a few distinct chemical species whose energies, if they could be independently changed, would achieve a faster net reaction rate to the product of interest. For example, when there is a single “rate-determining step”, the DRC for its transition state (TS) is 1, which means (by definition) that if this TS’s energy could be decreased by kBT (where kB is Boltzmann’s constant and T is temperature), the net rate would increase by a factor of e. Because the (relative) energies of these key adsorbed intermediates and transition states can be adjusted by modifying the catalyst or solvent, or even a reactant’s molecular structure, the DRC values pr...

Towards the atomic-scale characterization of isolated iron sites confined in a nitrogen-doped graphene matrix

Atomic scale characterization of the surface structure of powder catalysts is essential to the identification of active sites, but remains a major challenge in catalysis research. We described here a procedure that combines atomic force microscopy (AFM), operated in air, and scanning tunneling microscopy (STM), operated in UHV, to obtain the atomic structure and local electronic properties of powder catalysts. The atomically dispersed Fe-N-C catalyst was used as an example, which was synthesized by low temperature ball milling methods. We discussed the effect of solvents in the dispersion of powder catalysts on a planar support, which is key to the subsequent atomic characterization. From the morphology, atomic structure and local electronic properties of the Fe-N-C catalyst, our combined measurements also provide an insight for the effect of ball milling in the preparation of atomically dispersed metal catalysts.

Cover Picture: German Catalysis Society (GeCatS) (ChemCatChem 4/2017)

The Front Cover shows a monument of Goethe and Schiller, two famous German poets, who both lived in Weimar. Weimar has a strong connection to the German catalysis community as hosting city of the Jahrestreffen Deutscher Katalytiker (Annual Meeting of German Catalysis Researchers), which celebrates its 50th anniversary this year. The picture illustrates also the development of catalysis from the Döbereiner lighter in the beginning to the application in large industrial plants. More information can be found in the GeCatS Society Profile by M. Muhler on page 525 in Issue 4, 2017 (DOI: 10.1002/cctc.201700117).

Interfaces in Heterogeneous Catalysts: Advancing Mechanistic Understanding through Atomic-Scale Measurements.

Developing novel catalysts with high efficiency and selectivity is critical for enabling future clean energy conversion technologies. Interfaces in catalyst systems have long been considered the most critical factor in controlling catalytic reaction mechanisms. Interfaces include not only the catalyst surface but also interfaces within catalyst particles and those formed by constructing heterogeneous catalysts. The atomic and electronic structures of catalytic surfaces govern the kinetics of binding and release of reactant molecules from surface atoms. Interfaces within catalysts are introduced to enhance the intrinsic activity and stability of the catalyst by tuning the surface atomic and chemical structures. Examples include interfaces between the core and shell, twin or domain boundaries, or phase boundaries within single catalyst particles. In supported catalyst nanoparticles (NPs), the interface between the metallic NP and support serves as a critical tuning factor for enhancing catalytic activity. Surface electronic structure can be indirectly tuned and catalytically active sites can be increased through the use of supporting oxides. Tuning interfaces in catalyst systems has been identified as an important strategy in the design of novel catalysts. However, the governing principle of how interfaces contribute to catalyst behavior, especially in terms of interactions with intermediates and their stability during electrochemical operation, are largely unknown. This is mainly due to the evolving nature of such interfaces. Small changes in the structural and chemical configuration of these interfaces may result in altering the catalytic performance. These interfacial arrangements evolve continuously during synthesis, processing, use, and even static operation. A technique that can probe the local atomic and electronic interfacial structures with high precision while monitoring the dynamic interfacial behavior in situ is essential for elucidating the role of interfaces and providing deeper insight for fine-tuning and optimizing catalyst properties. Scanning transmission electron microscopy (STEM) has long been a primary characterization technique used for studying nanomaterials because of its exceptional imaging resolution and simultaneous chemical analysis. Over the past decade, advances in STEM, that is, the commercialization of both aberration correctors and monochromators, have significantly improved the spatial and energy resolution. Imaging atomic structures with subangstrom resolution and identifying chemical species with single-atom sensitivity are now routine for STEM. These advancements have greatly benefitted catalytic research. For example, the roles of lattice strain and surface elemental distribution and their effect on catalytic stability and reactivity have been well documented in bimetallic catalysts. In addition, three-dimensional atomic structures revealed by STEM tomography have been integrated in theoretical modeling for predictive catalyst NP design. Recent developments in stable electronic and mechanical devices have opened opportunities to monitor the evolution of catalysts in operando under synthesis and reaction conditions; high-speed direct electron detectors have achieved sub-millisecond time resolutions and allow for rapid structural and chemical changes to be captured. Investigations of catalysts using these latest microscopy techniques have provided new insights into atomic-level catalytic mechanisms. Further integration of new microscopy methods is expected to provide multidimensional descriptions of interfaces under relevant synthesis and reaction conditions. In this Account, we discuss recent insights on understanding catalyst activity, selectivity, and stability using advanced STEM techniques, with an emphasis on how critical interfaces dictate the performance of precious metal-based heterogeneous catalysts. The role of extended interfacial structures, including those between core and shell, between separate phases and twinned grains, between the catalyst surface and gas, and between metal and support are discussed. We also provide an outlook on how emerging electron microscopy techniques, such as vibrational spectroscopy and electron ptychography, will impact future catalysis research.

Advances in methane conversion processes

In this short review, we highlight the recent advances in methane conversion processes at high and low temperatures. Methane conversion processes are of great importance in achieving a crude-oil independent supply of energy, fuels and chemicals for the future. Direct conversion of methane into chemicals and fuels has been often considered as the “holy grail” of current catalysis research due to the unreactive nature of methane, which makes targeted chemical transformations to fuels and chemicals very challenging. We discuss the progress in developing heterogeneous catalytic and electrocatalytic systems to overcome this challenge. We conclude by providing a perspective on the future of this area of research.

On Spatial Control in Heterogeneous Multifunctional Catalysts

Diversity of heterogeneous catalysis as a discipline spanning many scales resulted in less attention to the meso-scale. An important issue in catalysis research, often overlooked by the academic community, is preparation of shaped bodies in a systematic way unraveling the scientific basis of such preparation. In particular presence of binders in shaped catalysts could influence reactions on bifunctional catalysts. Several challenges related to efficient spatial arrangement of active catalytic phases with a controlled distance between active sites are discussed.

Perspective: On the active site model in computational catalyst screening.

First-principles screening approaches exploiting energy trends in surface adsorption represent an unparalleled success story in recent computational catalysis research. Here we argue that our still limited understanding of the structure of active sites is one of the major bottlenecks towards an ever extended and reliable use of such computational screening for catalyst discovery. For low-index transition metal surfaces, the prevalently chosen high-symmetry (terrace and step) sites offered by the nominal bulk-truncated crystal lattice might be justified. For more complex surfaces and composite catalyst materials, computational screening studies will need to actively embrace a considerable uncertainty with respect to what truly are the active sites. By systematically exploring the space of possible active site motifs, such studies might eventually contribute towards a targeted design of optimized sites in future catalysts.

Günther Wilke (1925-2016).

Günther Wilke (1925-2016).

Size control of nanoparticles by multiple-pulse laser ablation

Bare nanoparticles synthesized by laser ablation in water have found their application in catalysis, spectroscopy and biomedical research fields. In this perspective, how to efficiently produce stable nanoparticles with controllable size is an important topic and has attracted a lot of interests. Here, we introduce a multiple-pulse laser as the ablation source. By changing the number of sub-pulses, the average size of nanoparticles can be tuned in a broad range from ∼120nm to ∼4nm. The demonstration in this article may offer a new approach to fabricate ultrafine nanostructures and also help the scientific study of the mechanism in laser ablation.

Catalysis, Anytime, Anywhere.

Harder, better, faster, stronger: This editorial features 2016 in review, a new look Editorial Board, journal innovation and travel plans—a little of everything worth sharing. Here at ChemCatChem, we enter our ninth year with a rejuvenated Editorial Board, fresh co-Chairmen, and excellent catalysis research! 2016 was another year of significant progress for ChemCatChem. We are grateful for so much; not least the great support and feedback of our readership. This year, we received more papers and published more papers than ever before. We have attended conferences, given lectures, and sponsored prizes. So what happened in 2016? ChemCatChem continues to flourish in this rich world of catalysis research. We received more manuscripts than ever before from nearly 60 countries. Research from China continues to represent the lion's share of submissions followed by India, Germany, USA, and Japan. As a journal we continue to question our methods and practices. Four main points have come out of this for 2016, the introduction of the Accepted Article, the ORCID identifier, clarity for author contributions, and plagiarism detection software. Accepted Articles provide the potential for our authors to publish their research within hours of acceptance. Authors are now offered the opportunity to publish their accepted revised manuscript to Wiley Online Library at the same time as uploading their production material. Once the files are uploaded, the process of uploading to the website is automatic and processed in batches. Online Accepted Articles are fully searchable, accessible, and citable. With their submission to ChemCatChem, authors are now requested to complete the “conflict of interest“ section as part of the submission process. In addition, we now ask for the individual contributions of the authors named on a submission to be noted. With this issue, we are introducing a new feature in ChemCatChem. The Catalysis Society Profile highlights a different catalysis society or division from around the world. A short overview and Q&A section to introduce the society to the readers is followed by a freestyle section to promote upcoming events such as conferences and awards. If your catalysis society wishes to be promoted in this way, please get in touch with the editorial office. In 2016, we attended many excellent conferences and we would like to thank them all for their warm welcome. We found each one to be an excellent opportunity to meet and engage with our readership. For 2017, we will again be attending a range of conferences: Netherlands’ Catalysis and Chemistry Conference, the 50th meeting of the German Catalysis Society, the North American Catalysis Society Meeting, Spanish Catalysis Society Meeting, and EUROPACAT. We hope to see many of you, our readers and authors, there! On behalf of the co-Chairmen (old and new), ChemPubSoc Europe, the editorial office, and Wiley-VCH, I would just like to wish all our authors and readers a most awesome 2017.

Gabor A. Somorjai Award for Creative Research in Catalysis: John E. Bercaw

NATIONAL AWARDS Gabor A. Somorjai Award for Creative Research in Catalysis: John E. Bercaw ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2017, 95 (1), pp 36–50January 2, 2017Cite this:C&EN 95, 1, 36-50John E. Bercaw (Credit: Bob Paz )Figure1of1Sponsor: Gabor A. & Judith K. Somorjai Endowment Fund Citation: For the elucidation of detailed mechanisms of organometallic reactions that comprise catalytic cycles. Current position: Centennial Professor Emeritus of Chemistry, California Institute of Technology Education: B.S., chemistry, North Carolina State University; Ph.D., chemistry, University of Michigan, Ann Arbor Bercaw on his scientific role model: “Harry Gray is one of my scientific role models. In addition to watching with amazement his scientific accomplishments, I have marveled at his enthusiasm, modesty, generosity, and love of interacting with students. He is truly a great man.” What his colleagues say: “Bercaw has made path-breaking contributions to developing and elucidating new homogenous catalytic reactions. His fundamental work in olefin polymerization catalysis and catalytic alkane oxidation is without equal.”—Maurice Brookhart, University of North Carolina, Chapel Hill

Development of Batch and Flow Immobilized Catalytic Systems with High Catalytic Activity and Reusability.

My mission in catalysis research is to develop highly active and reusable supported catalytic systems in terms of fundamental chemistry and industrial application. For this purpose, I developed three types of highly active and reusable supported catalytic systems. The first type involves polymeric base-supported metal catalysts: Novel polymeric imidazole-Pd and Cu complexes were developed that worked at the mol ppm level for a variety of organic transformations. The second involves catalytic membrane-installed microflow reactors: Membranous polymeric palladium and copper complex/nanoparticle catalysts were installed at the center of a microtube to produce novel catalytic membrane-immobilized flow microreactor devices. These catalytic devices mediated a variety of organic transformations to afford the corresponding products in high yield within 1-38 s. The third is a silicon nanowire array-immobilized palladium nanoparticle catalyst. This device promoted a variety of organic transformations as a heterogeneous catalyst. The Mizoroki-Heck reaction proceeded with 280 mol ppb (0.000028 mol%) of the catalyst, affording the corresponding products in high yield.

Metal–Metal Bonds in Catalysis

Transition metals can assemble to form multinuclear complexes by engaging in direct metal-to-metal interactions. Metal–metal covalent bonds provide a large perturbation in electronic structure, relative to mononuclear metal ions, and the unique properties of these dinuclear fragments can be harnessed in a broad range of applications—for example, as chromophores in photochemical processes, redox centers in molecular electronics, or structural elements in metal–organic materials. There is a growing body of evidence that metal–metal bonds may also be formed under conditions relevant to catalysis and play a key role in transformations that were previously assumed to only involve mononuclear species. These findings have stimulated interest in characterizing multinuclear reaction pathways and developing well-defined multinuclear platforms as catalytic active sites. In this Perspective, we present case studies in this emerging area of catalysis research, emphasizing the impact of metal–metal bonding in either en...