Download or read book Design of Selective Palladium based Catalyst for Direct Synthesis of Hydrogen Peroxide written by Tianze Xie and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct synthesis of hydrogen peroxide (DSHP) is a promising alternative to the current industrial method for H2O2 production (Riedl-Pfleiderer process). Pd-based catalyst is known to be highly active for DSHP while the selectivity fails to satisfy industrial requirement. Pd-metal alloys receive most attention to achieve high H2O2 selectivity, whereas to best of our knowledge, no effort has been devoted to the incorporation of light element (e.g., B, C, P, and S) into Pd for DSHP. The achievable concentration of H2O2 from DSHP process is far below the industrial requirement, primarily due to the significant extent of degradation reactions. Decomposition of H2O2 to water and oxygen is a dominant secondary reaction in DSHP and critical in other oxidation chemistries. The mechanism of Pd-catalyzed H2O2 decomposition is still debated. This dissertation mainly covers two topics: (i) development and optimization of selective Pd carbide catalyst for DSHP and (ii) mechanism study of Pd-catalyzed H2O2 decomposition. We proposed a carbonization method to prepare interstitial Pd carbide catalyst as an alternative to the use of bimetallic catalyst for H2O2 synthesis. We carbonized silica-supported palladium catalyst through heat treatment in acetylene flow and the synthesized Pd-C material shows a 4-fold increase in H2O2 selectivity but only with a half reduction in H2O2 formation rate compared with the parent metallic Pd catalyst. Both bulk carbon and surface carbon species contribute to the increased selectivity towards H2O2. The fragments of hydrocarbon species adsorb on catalyst surface after C2H2 treatment and break up contiguous Pd ensembles. The isolated Pd active site is more selective for H2O2 formation. DFT calculations demonstrate the subsurface carbon has an electronic effect on Pd and increases the activation barrier for the O-O bond breaking. Consistently, the measured apparent activation energy increases for both H2O2 formation and H2O formation over Pd carbide catalyst, while the impact of carbonization is more significant on H2O formation. The Pd carbide catalyst is simple and cheap to prepare, facile to regenerate by O2 and H2 and also exhibits a comparable selectivity increase as the state-of-the-art bimetallic catalyst. We optimized the kinetic performance of Pd carbide catalyst by pre-treatment (carbonization time, temperature, and gas identity) and post-treatment (H2 and O2 treatment). With increased carbonization time or temperature, the selectivity towards H2O2 increases while the yield of H2O2 initially increases and then decreases. Pd carbide catalyst shows higher H2O2 selectivity at the same bulk carbon content after C2H2 treatment than using CO and CH3OH vapor as carbonization gas. We attribute this observation to the different identity of the carbon species adsorbed on catalyst surface. Reduction of Pd carbide catalyst by H2 enhances the activity for H2O2 formation whereas decreases the H2O2 selectivity. We demonstrated the regenerability of Pd and Pd carbide catalyst through oxygen and hydrogen post-treatment. Addition of methanol into solvent (water) increases the H2O2 selectivity on both Pd and Pd carbide, while the impact is more significant on Pd than Pd carbide. We propose the role of organic alcohol as solvent resembles the carbonization treatment to the Pd catalyst that surface adsorbed carbon species isolate the Pd active site and exert an ensemble effect on inhibiting O-O bond breaking. We summarize the activity and selectivity of Pd carbide catalysts optimized in this work follow a volcano relationship. We proposed a water-assisted mechanism involving kinetically relevant proton electron transfer (PET) reactions for Pd-catalyzed H2O2 decomposition. The proposed mechanism is consistent with the observed saturation kinetics, primary kinetic isotope effect, particle size effect, and influence of proton concentration. Larger particles have increased reactivity towards H2O2 decomposition due to increased electron transfer to H2O2 relative to smaller Pd particles. Insignificant influence of proton concentration on decomposition rate indicates water molecule rather than H+ serves as proton donor and participates the kinetically relevant PET step. Kinetic coupling of Pd-catalyzed H2O2 decomposition with the Fenton reaction (reactive oxygen species oxidation) demonstrates surface adsorbed *H2O2 and *HOO species are the most abundant reactive intermediate. These results will support the rational design of selective catalyst for DSHP by demonstrating catalyst properties that can suppress secondary degradation reactions to produce targeted industrial grade H2O2.

Download or read book Palladium tin Catalysts for the Direct Synthesis of H2O2 with High Selectivity written by and published by . This book was released on 2016 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 represents a potentially atom-efficient alternative to the current industrial indirect process. We show that the addition of tin to palladium catalysts coupled with an appropriate heat treatment cycle switches off the sequential hydrogenation and decomposition reactions, enabling selectivities of>95% toward H2O2 . This effect arises from a tin oxide surface layer that encapsulates small Pd-rich particles while leaving larger Pd-Sn alloy particles exposed. In conclusion, we show that this effect is a general feature for oxide-supported Pd catalysts containing an appropriate second metal oxide component, and we set out the design principles for producing high-selectivity Pd-based catalysts for direct H2O2 production that do not contain gold.

Download or read book Preparation and Characterisation of Gold and Palladium Based Catalysts for the Direct Synthesis of Hydrogen Peroxide written by James Pritchard and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: I The research presented in this thesis describes the direct synthesis of hydrogen peroxide from H2 and O2 using supported gold-palladium based catalysts. The direct synthesis process offers a green and sustainable approach compared to the anthraquinone autoxidation (AO) process, which is currently used on an industrial scale to produce >95% H2O2 worldwide. The work presented in this thesis is an attempt to examine the direct synthesis process in terms of determining optimum catalyst compositions for potential scale-up in the near-future. The primary aim of this investigation is centred on catalyst design and characterisation. The first part of this work is a catalyst optimisation study for 2.5 wt% Au-2.5 wt% Pd/TiO2, and involved changing the amount of water used in the catalyst preparation, in this case wet impregnation. It was found that the addition of small amounts of water resulted in approximately 100% enhancement in activity for TiO2-supported catalysts but not for carbonsupported Au-Pd catalysts. The rate of Au/Pd uptake was contrasted and it was determined that the isoelectric point of the support was highly influential. While the activity can be enhanced for TiO2-supported catalysts, both catalyst nanostructure and stability were detrimentally affected by the addition of water during the impregnation step. The second part of this work is focussed on understanding the precise nature of the acid pre-treatment effect, where treatment of a carbon support in dilute nitric acid prior to the impregnation of Au and Pd precursors can result in the complete switching-off of sequential H2O2 hydrogenation activity over the catalyst. Characterisation and heat treatment studies gave an improved understanding of the relationship between Au/Pd and the carbon support. The next part of the study addresses the use of a colloidal immobilisation method to pre-fabricate Au-Pd 'designer' nanoparticles onto supports and is accompanied by extensive advanced aberration corrected electron microscopy studies. The effect of acid pre-treating silica based supports is then considered for catalysts prepared by wet-impregnation, specifically the fact that acid pre-treatment of silica is required to induce synergy between Au and Pd metals for the direct synthesis of hydrogen peroxide. The final part of this work considers the effect of introducing a third metal into the catalyst design, specifically the addition of Pt to Au/Pd compositions. An extensive catalyst screening study is undertaken for Au-Pd-Pt/CeO2 catalysts.

Download or read book XAFS Techniques for Catalysts Nanomaterials and Surfaces written by Yasuhiro Iwasawa and published by Springer. This book was released on 2016-10-19 with total page 545 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a comprehensive, theoretical, practical, and thorough guide to XAFS spectroscopy. The book addresses XAFS fundamentals such as experiments, theory and data analysis, advanced XAFS methods such as operando XAFS, time-resolved XAFS, spatially resolved XAFS, total-reflection XAFS, high energy resolution XAFS, and practical applications to a variety of catalysts, nanomaterials and surfaces. This book is accessible to a broad audience in academia and industry, and will be a useful guide for researchers entering the subject and graduate students in a wide variety of disciplines.

Download or read book Mechanisms Active Sites and Promoters for the Direct Synthesis of Hydrogen Peroxide on Pd based Catalysts written by Anthony David Plauck and published by . This book was released on 2016 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: The widespread use of hydrogen peroxide (H2O2) for catalytic oxidations is limited by the wasteful process by which it is currently produced: the anthraquinone process. The direct synthesis of H2O2 (DSHP) is a promising alternative process. One primary technical obstacle to its commercialization is the identification of sufficiently active and selective heterogeneous catalysts. Although Pd is a promising active component that is used in most catalyst formulations, two factors have restricted the search directions for improved DSHP catalysts to experimental trial and error: (i) the reaction mechanisms are not resolved, and (ii) the active site requirements are poorly understood. Addressing these factors is complicated by the existence of multiple side reactions and the inherent complexities of heterogeneous catalysts and the DSHP reaction environment. In this dissertation, we employ density functional theory calculations to develop an atomic-scale understanding of the DSHP on Pd-based catalysts. We propose reaction mechanisms and analyze Pd's intrinsic reactivity toward forming H2O2 versus H2O from H2 and O2. We also develop an experimentally-consistent microkinetic model that describes H2O2 decomposition on Pd; one of the major drawbacks of Pd catalysts is high activity toward this undesirable reaction. Through these studies we highlight specific mechanistic challenges, including the identification of likely rate-limiting steps. We then consider how catalyst structure and composition can be modified to mitigate these challenges. We analyze the impact of the coordinative saturation of the Pd surface, the role of halides and Au as catalytic promoters, and the effect of phase transformations induced by the reaction environment. Our work demonstrates the utility of computational chemistry in deconvoluting complex catalytic systems - especially when coupled with experimental and microkinetic analyses. The results can potentially be used to build a framework that guides the search for new DSHP catalysts.

Download or read book Selective Oxidation Processes written by American Chemical Society. Division of Petroleum Chemistry and published by . This book was released on 1965 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Direct Synthesis of Hydrogen Peroxide Using Bimetallic Gold and Palladium Supported Catalysts written by Greg Shaw and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis the direct synthesis of hydrogen peroxide from hydrogen and oxygen using gold-palladium supported catalysts is described. The direct route presents a greener and sustainable alternative to the current industrial manufacture process. This work aims to meet industrial requirements set by Solvay® which would make the direct process industrially viable. The drawback preventing the requirements being met is the reaction of hydrogen and oxygen over a catalyst can yield water as well as hydrogen peroxide. Once H2O2 is formed, it can be consumed by either reduction or decomposition. Thus, the rates of the subsequent reactions must be minimized to increase the selectivity and therefore H2O2 concentration to a desirable level. Aspects of the catalyst design and reaction variables have been studied over three results chapters. Firstly, the thermal treatment conditions have been altered, ultimately producing a catalyst with no activity to the H2O2 consumption under standard conditions. Switching off H2O2 hydrogenation was concluded to be due to an increase in Pd2+, isolating active Pd0 species. Secondly, active catalysts to both the synthesis and hydrogenation of H2O2 have been produced with no halide; the addition of halide has been shown to decrease hydrogenation activity while maintaining synthesis activity. Finally, a biphasic solvent system and a constant flow of gases through the reaction medium have been examined in order to produce higher H2O2 concentrations. In the former case H2O2 is extracted in-situ from an immiscible organic phase. The production of a 3 wt% H2O2 solution highlights the potential of such a system. In the latter case a semi-continuous flow reactor is utilised increasing the H2O2 concentration up to ca. 1 wt% (from ca. 0.2 wt%). The reactor allowed H2 selectivity and H2O concentration to be measured as a function of time, thus providing greater insight into catalyst activity.

Download or read book The Direct Synthesis of Hydrogen Peroxide Using Gold and Palladium Based Catalysts written by Marco Piccinini and published by . This book was released on 2012 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electrochemical Oxygen Reduction written by Pei Kang Shen and published by Springer Nature. This book was released on 2021-01-16 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses systematically the theoretical research and the applications of electrochemical oxygen reduction. Oxygen reduction reaction is a common issue in electrochemistry, but is also an important process involved in the field of energy, cryogenic fuel cells, metal–air cells, oxygen sensors and hydrogen peroxide preparation. This book is divided into 6 chapters; it starts with a description of dynamic mechanisms, followed by a detailed introduction on the related experimental methods and related catalyst preparation technology. By providing the basic methods and testing techniques, and by demonstrating their applications, it helps readers gain a better understanding of oxygen reduction reactions, making it a valuable resource for the industrialization of scientific research achievements. Accordingly, the book appeals to a broad readership, particularly graduate students, those working at universities and research organizations, and industrial researchers.

Download or read book Sustainable Flow Chemistry written by Luigi Vaccaro and published by John Wiley & Sons. This book was released on 2017-04-10 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt: This ready reference not only presents the hot and emerging topic of modern flow chemistry, it is also unique in illustrating the important connection to sustainable chemistry. Focusing on more sustainable methods and applications, the text extensively covers every important field from reaction time optimization to waste minimization, and from safety improvements to microwave applications. In addition, green metrics are presented as a key aspect of the book, helping readers to evaluate the efficiency of flow technologies and their impact on the overall efficiency of a chemical process. An invaluable handbook for every chemist working in the laboratory, whether in academia or industry.

Download or read book The 100 Most Important Chemical Compounds written by Richard L. Myers and published by Bloomsbury Publishing USA. This book was released on 2007-08-30 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: What is a chemical compound? Compounds are substances that are two or more elements combined together chemically in a standard proportion by weight. Compounds are all around us - they include familiar things, such as water, and more esoteric substances, such as triuranium octaoxide, the most commonly occurring natural source for uranium. This reference guide gives us a tour of 100 of the most important, common, unusual, and intriguing compounds known to science. Each entry gives an extensive explanation of the composition, molecular formula, and chemical properties of the compound. In addition, each entry reviews the relevant chemistry, history, and uses of the compound, with discussions of the origin of the compound's name, the discovery or first synthesis of the compound, production statistics, and uses of the compound.

Download or read book Characterization of Heterogeneous Catalysts written by Francis Delannay and published by Marcel Dekker. This book was released on 1984 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Direct Synthesis of Hydrogen Peroxide Using Bimetallic Gold and Palladium Supported Catalysts written by Adeeba Akram and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Solar to Chemical Conversion written by Hongqi Sun and published by John Wiley & Sons. This book was released on 2021-04-29 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: This comprehensive book systematically covers the fundamentals in solar energy conversion to chemicals, either fuels or chemical products. It includes natural photosynthesis with emphasis on artificial processes for solar energy conversion and utilization. The chemical processes of solar energy conversion via homogeneous and/or heterogeneous photocatalysis has been described with the mechanistic insights. It also consists of reaction systems toward a variety of applications, such as water splitting for hydrogen or oxygen evolution, photocatalytic CO2 reduction to fuels, and light driven N2 fixation, etc. This unique book offers the readers a broad view of solar energy utilization based on chemical processes and their perspectives for future sustainability.

Download or read book Direct Synthesis of Hydrogen Peroxide Using Monometallic and Bimetallic Pd Based Catalysts Supported on TiO2 written by Dávid Kovačič and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modern Heterogeneous Oxidation Catalysis written by Noritaka Mizuno and published by John Wiley & Sons. This book was released on 2009-11-18 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: Filling a gap in the current literature, this comprehensive reference presents all important catalyst classes, including metal oxides, polyoxometalates, and zeolites. Readers will find here everything they need to know -- from structure design to characterization, and from immobilization to industrial processes. A true must-have for anyone working in this key technology.

Download or read book Catalysis By Gold written by Geoffrey C Bond and published by World Scientific. This book was released on 2006-08-15 with total page 383 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gold has traditionally been regarded as inactive as a catalytic metal. However, the advent of nanoparticulate gold on high surface area oxide supports has demonstrated its high catalytic activity in many chemical reactions. Gold is active as a heterogeneous catalyst in both gas and liquid phases, and complexes catalyse reactions homogeneously in solution. Many of the reactions being studied will lead to new application areas for catalysis by gold in pollution control, chemical processing, sensors and fuel cell technology. This book describes the properties of gold, the methods for preparing gold catalysts and ways to characterise and use them effectively in reactions. The reaction mechanisms and reasons for the high activities are discussed and the applications for gold catalysis considered./a