Innovative Applications of Mo(W)-Based Catalysts in the Petroleum and Chemical Industry: Emerging Research and Opportunities Hui Ge Chinese Academy of Sciences, China Xingchen Liu Chinese Academy of Sciences, China Shanmin Wang Oak Ridge National Laboratory, USA Tao Yang China University of Petroleum, China Xiaodong Wen Synfuels China, China A volume in the Advances in Chemical and Materials Engineering (ACME) Book Series Published in the United States of America by IGI Global Engineering Science Reference (an imprint of IGI Global) 701 E. Chocolate Avenue Hershey PA 17033 Tel: 717-533-8845 Fax: 717-533-8661 E-mail: [email protected] Web site: http://www.igi-global.com Copyright © 2017 by IGI Global. All rights reserved. No part of this publication may be reproduced, stored or distributed in any form or by any means, electronic or mechanical, including photocopying, without written permission from the publisher. Product or company names used in this set are for identification purposes only. Inclusion of the names of the products or companies does not indicate a claim of ownership by IGI Global of the trademark or registered trademark. Library of Congress Cataloging-in-Publication Data Library of Congress Cataloging-in-Publication Data Names: Ge, Hui, 1964- author. Title: Innovative applications of Mo(W)-based catalysts in the petroleum and chemical industry : emerging research and opportunities / by Hui Ge, Xingchen Liu, Shanmin Wang, Tao Yang, and Xiaodong Wen. Description: Hershey, PA : Engineering Science Reference, [2017] | Includes bibliographical references. Identifiers: LCCN 2016057549| ISBN 9781522522744 (hardcover) | ISBN 9781522522751 (ebook) Subjects: LCSH: Catalysis. | Catalytic reforming. | Molybdenum compounds--Industrial applications. | Chalcogenides--Industrial applications. | Green chemistry. Classification: LCC TP156.C35 G423 2017 | DDC 660/.2995--dc23 LC record available at https:// lccn.loc.gov/2016057549 This book is published in the IGI Global book series Advances in Chemical and Materials Engineering (ACME) (ISSN: 2327-5448; eISSN: 2327-5456) British Cataloguing in Publication Data A Cataloguing in Publication record for this book is available from the British Library. All work contributed to this book is new, previously-unpublished material. The views expressed in this book are those of the authors, but not necessarily of the publisher. Advances in Chemical and Materials Engineering (ACME) Book Series ISSN:2327-5448 EISSN:2327-5456 Editor-in-Chief: J. 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Dichalcogenides.Nanosheets...................................................................................1 ; ; Chapter 2 ; The.Fundamental.Research.and.Application.Progress.of.2D.Layer.Mo(W) S2-Based.Catalyst.................................................................................................31 ; ; Chapter 3 ; 3D.Catalysts.of.Mo(W).Carbide,.Nitride,.Oxide,.Phosphide,.and.Boride...........53 ; ; Chapter 4 ; Low-Dimensional.Molybdenum-Based.Catalytic.Materials.from.Theoretical. Perspectives.........................................................................................................100 ; ; Chapter 5 ; Summary.and.Perspectives.................................................................................129 ; ; Related Readings...............................................................................................137 ; ; About the Authors.............................................................................................158 ; ; Index...................................................................................................................160 ; ; vi Preface The discovery of graphene has attracted tremendous research interest in two- dimensional (2D) layered materials characterized with strong covalent bond- ing in intralayer and weak van der Waals interaction between interlayers. Among them, Mo and W dichalcogens (e.g. WS , MoS , MoSe , MoTe ) have 2 2 2 2 been deeply and extensively explored due to their special properties and easy fabrication. These 2D materials with reduced dimensionality in vertical di- rection exhibit unique catalytic properties. For example, the band structures can significantly be altered when these materials are reduced from bulk to the single-layer limit, giving rise to great opportunities to fabricate catalysts with excellent performance. Besides, these 2D materials can be semiconduc- tors, metals, and superconductors, and they represent a versatile and ideal system for exploring catalysis at the limit of atomic scale, and have the po- tential to open up exciting new opportunities beyond the reach of existing materials and enable advances across diverse disciplines, such as electronics, photonics, energy and catalysis. Typical layer of Mo or W dichalcogenide features the “sandwich” layer, which consist typically of one plane of hexagonally packed metal atoms sandwiched by two planes of chalcogenide atoms. The sandwich layers are vertically stacked and loosely bonded by weak van der Waals forces to form the 3D bulk material. This high anisotropy induces the structure-sensitive catalytic phenomena. However, a material with fixed structures may not exhibit versatile applications. With the unique anisotropy, the physical and chemical properties of 2D layered Mo(W) dichalcogenides can be tuned easily through different strategies such as reducing dimensions, intercalation, and alloying and new catalytic properties can be achieved. For example, through the intercalation of guest alkali ions, the carrier densities of 2D layer Mo(W) dichalcogenides can be increased by multiple orders of magnitude, compa- nied by a transformation of the Mo(W) dichalcogenides from semiconductor 2H phase to 1T metal transition. This results in the large improvement of hydrogen evolution reaction (HER). vii Another interesting feature is that Mo(W) dichalcogenide 2D layers can constitute lateral or vertical heterostructures. Vertical heterostructures which are held together by van der Waals forces can be fabricated by almost arbitrary combinations using relative simple synthesizing techniques. However, lateral heterostructures with two materials linked by covalent bonds are more difficult to manufacture. These heterostructures of 2D Mo(W) dichalcogenide layers create superlattice and complexity with totally new functions for electric- and photo-catalysis. Therefore, Mo(W) dichalcogenide 2D heterostructure prepared by lateral or vertical growth or alloying provide almost unlimited opportunities to synthesize excellent catalysts with tunable properties. Besides dichalcogenides/dichalcogenides heterostructures, the flexible van der Waals interaction can also allow the creation of diverse heterostructures between 2D Mo(W) dichalcogenides and other atomic layered materials, including graphene, carbon nitride and boron nitride etc. The formation of such versatile heterostructures can enable the design of entirely new “interbedded” catalysts. To utilize the full potential of 2D Mo or W dichalcogenide materials, it is necessary to develop strategies for synthesizing these materials with a well-defined dimension, chemical composition, and heterostructure inter- face. The bottom-up approach of chemical vapour deposition (CVD) allows the growth of relatively high quality 2D layers on supported surfaces with a well-defiined lateral size and layer thickness. Hydrothermal or solvothermal synthesis is also promising but with only little investigation. Among the top- down approaches, the mechanical exfoliation of bulk crystals have produced large areas of 2D Mo(W) dichalcogenides with variable thicknesses down to a single lattice unit, and has been utilized for initial fundamental studies. It is however limited by the very low throughput. The chemical and solvent exfoliation approach can allow for the production of a relatively large quantity of 2D materials. This are now the only possible method for preparing the industrial 2D catalysts. But the resulting materials may be contaminated with impurity doping or have a poor control of the dimension size and thickness. Thus the synthesizing approaches still need to be developed. Mo(W)S -based layer catalysts in face has long been used in petroleum and 2 chemical industry before the spring up of the graphene. They are of critical importance in the refining processes, such as hydrotreatment, hydrocrack- ing and hydrogenation. The hydrotreatment is seen as an inheritance of coal technologies developed in Germany at the beginning of the twentieth century. In 1924 researchers of BASF found that transition metal sulfides were ef- ficient catalysts for coal hydro-liquefaction and screened out molybdenum sulfide used in these processes. After the Second World War, instead of the coal conversion, petroleum refining got fast development. Molybdenum viii sulfides promoted by cobalt and supported on alumina were firstly used in the USA as the catalysts for the hydrotreating processes which simultane- ous removed sulfur, nitrogen and metal impurities in oil streams. Since that time, new combinations of supported sulfides (such as NiMo and NiW) had also been synthesized for more specific applications, e.g. hydrogenation and hydrocracking. The oil crises in 1973 and 1979 stimulated a surge of researches related to these catalysts and processes in both academic laboratories and refining industries with the objective of developing more active and selective catalysts. During 1980s and 90s, accompanying with the advance in analytic and char- acterized technologies, important discoveries were reported in the literature. For example, using Mössbauer spectroscopy, the interaction of Co and Mo was elucidated as the Co-Mo-S active phase responsible for the promotion in hydrodesulfurization (HDS) catalytic activity. It was proposed that these Co-Mo-S (and also Ni-Mo-S) structures are small MoS -like nanocrystals 2 with the promoter atoms located at the edges of the MoS layers. Further 2 investigation suggested that Co atoms are located in the same plane as Mo, but that their local coordination is different. However for a long-time it is difficult to address the issue of the detailed edge structure of unpromoted and promoted MoS 2D layer, as atomic-resolved 2 structures could not be detected. Entering 2000s, with the fast advance in characterization at atomic level, some breakthroughs were achieved. By scanning tunneling microscopy (STM), the real-space structures of MoS and 2 Co(Ni) promoted MoS nanoclusters grown on flat model substrates were 2 imaged. It was possible, for the first time, to reveal the equilibrium morphol- ogy of these 2D nanoclusters. And the brim sites, which is located near the edge, was firstly discovered by the STM experiment, and DFT calculation suggested it as the active centers for hydrogenation reaction due to the metal- lic property. By high-angle annular dark field scanning tunneling electron microscopy (HAADFSTEM), additional information on the morphology of Mo(W)S based nanostructures have also been obtained. Furthermore, with 2 the combination of these new technologies, it is now possible to elucidate the detailed Co(Ni)Mo(W)S structure, such as the layer edges, the sulfur 2 coverage and the sulfur vacancies or defects, which are considered to be responsible for the catalytic properties. Based on the rich understanding about the relation of structure and activity, now designing HDS catalysts for controlled structure and functionalities are becoming a trend. It appears that now science is catching up with technol- ogy. Before long, due to the lack of adequate characterized tools, a detailed fundamental understanding of Mo(W)S based catalysts and their reaction 2 ix mechanisms was unavailable. At that time, catalyst development was to a large extent based on the “trial-and-error” experimentation. Although the activity and selectivity of Mo(W)S based catalyst have 2 been largely improved, development of better catalysts for hydrotreatment is still urgent. Environmental regulation in many countries requires the sulfur content in transport fuels down to about 10 ppm with the aim of reducing engine’s harmful emissions and improving air quality. And at the same times, the quality of transport fuels must be guaranteed. The ultra-desulfurization of gasoline streams needs to depress the hydrogenation of olefins to keep the octane number and decrease the hydrogen consumption. Meanwhile the production of ultra-low sulfur diesel (ULSD) necessitate some hydrogena- tion to aromatics increasing the cetane number. Thus the improvement of the hydrogenation selectivity will play a critical role in future hydrotreatment processing. The application of Mo(W)S based catalyst are also been extended to 2 other ranges, such as CO electric reduction, electro- and photo- catalytic 2 water-splitting, water-gas shift, and hydrotreating of bio-fuel. The vast emis- sions of CO through combustion of carbonaceous fuels, such as coal, oil, 2 natural gas and wood, have evoked social concerns due to the greenhouse gas effect. In the past few years, CO chemistry has become a very dynamic 2 area of research, hoping the use of emitted CO as a potential alternative 2 and economical C1 feedstock. The recent advances in the electric reduction of CO to CO in ion liquid using MoS layer flakes have demonstrated the 2 2 potential of Mo based catalyst in CO conversion. The hydrogen evolution 2 reaction (HER) via an electrocatalytic water-splitting method is considered a sustainable approach for hydrogen production if the electricity is from renew- able. The key problem now is seeking highly active electrocatalysts that can decrease the overpotential (η) and promote the HER performance. Pt is now the most efficient electrocatalyst for the HER, but its low abundance and high cost prevent large scale applications. Thus, the development of non-noble metal catalysts with low cost and high catalytic activity has attracted great research interest. In this field, a series of 3d transition metals, such as WN, WO , WS , MoO , MoS , MoB, MoP, MoSe and Mo C, have been exploited 2 2 2 2 2 2 as potential substitutes for Pt-based catalysts. Since Levy and Boudart reported in 1973 that tungsten carbides behaved similar to platinum for some types of reactions, a surge of research in these types of materials have occurred. It was evidenced that Mo(W) carbides in bulk or supported form, as well as promoted or not, are active for a lot of reactions that are usually catalyzed by noble metals. These carbides (e.g. Mo C and WC) are formed by the incorporation of carbon atoms into the 2