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In situ ambient-pressure X-ray photoelectron spectroscopy shows that CO2 introduced first at 300 K dissociates, whereas introducing the gases in the opposite order yields carboxyl (COOH) formation. The different pathways stem from initial surface conditions set by interaction of the first gas with Ni(111). Above 370–420 K, reactions are dominated by COOH formation, with graphitization above 470 K, suggesting dosage-dependent intermediates and enabling lower-energy catalyst design.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/selecting-reaction-pathways-of-co2-hydrogenation-on-ni111-by-kinetic-hindrance-associated-with-the-initial-surface-conditions-ambient-pressure-x-ray-photoelectron-spectroscopy/444044/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/selecting-reaction-pathways-of-co2-hydrogenation-on-ni111-by-kinetic-hindrance-associated-with-the-initial-surface-conditions-ambient-pressure-x-ray-photoelectron-spectroscopy/444044.png","ImageObject",300,407,{"name":92,"@type":93},"นรินทร์","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-03","2026-09-29",true,{"@type":102,"interactionType":103,"userInteractionCount":19},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"How does the gas dosage order affect CO2 hydrogenation intermediates on Ni(111)?","Question",{"text":112,"@type":113},"On Ni(111), the intermediates depend on whether CO2 is introduced before H2 or vice versa. Introducing CO2 first at 300 K leads to CO2 dissociation, while the opposite order produces COOH formation.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"What technique was used to observe the reaction pathways in this study?",{"text":117,"@type":113},"The study used in situ ambient-pressure X-ray photoelectron spectroscopy (APXPS) to monitor surface chemistry under a H2/CO2 mixed gas atmosphere.",{"name":119,"@type":110,"acceptedAnswer":120},"At what temperatures does COOH formation dominate, and what additional process occurs at higher temperatures?",{"text":121,"@type":113},"COOH formation dominates above about 370–420 K depending on gas pressure. Graphitization is associated with temperatures above about 470 K.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},444044,1790739879,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":19,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":139,"language":140,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":67,"update_tm":144,"read_time":41},2336475104957,"https://ap-avatar.wpscdn.com/avatar/22000c4c6bd8a5076e1?x-image-process=image/resize,m_fixed,w_180,h_180&k=1787554080175789136","This article is licensed under CC-BY 4.0   \n[http://pubs.acs.org/journal/acsodf](http://pubs.acs.org/journal/acsodf)  Article   \nSelecting Reaction Pathways of CO2 Hydrogenation on Ni(111) by Kinetic Hindrance Associated with the Initial Surface Conditions in the Treatment of H2/CO2 Mixed Gas, Studied by Ambient-Pressure X‑ray Photoelectron Spectroscopy  \nYu Murano, Masafumi Horio, Tetsuya Wada, Masashige Miyamoto, Yifu Liu, Yoshinori Kotani, Hiroyuki Yamane, Tetsuya Nakamura, Susumu Yamamoto, and Iwao Matsuda *  \n Cite This: ACS Omega 2025, 10, 58238−58249  \nRead Online  \n\n|  |  |  |  |  |  |\n| --- | --- | --- | --- | --- | --- |\n| ACCESS   | Metrics & More |  |  Article Recommendations |  | *sı Supporting Information |\n\nABSTRACT: Two types of surface reaction intermediates were observed in the presence of a H2/CO2 mixed gas on Ni(111), depending on the dosage order of the gases. The observations were carried out by in situ measurements with ambient-pressure X-ray photoelectron spectroscopy. When the CO2 gas was introduced at 300 K prior to the H2 gas, CO2 dissociation occurred. With the opposite order of gas dosage at the same temperature, carboxyl (COOH) formation was observed on the surface. The different reaction pathways originate from initial surface conditions due to the interaction between the first gas and Ni(111). In both cases, the reaction is dominated by COOH formation above 370−420 K, depending on the gas pressure, and is associated with graphitization above 470 K. The different reaction pathways followed according to the dosage order of the gases likely explain the various intermediates observed in previous studies. These results pave a new way to develop CO2 hydrogenation catalyst systems with lower energy consumption.  \n■ INTRODUCTION  \nActivation of carbon dioxide (CO2) for conversion into fuels or chemical feedstocks for a sustainable society is an important current topic in the chemical and energy industries. 1−3 CO2 can be a source to produce methane using a Ni catalyst. The CO2 methanation reaction is known as the Sabatier reaction: CO2 + 4 H2 → CH4 + 2 H2O.4,5 This reaction competes with the reverse water gas shift (RWGS) reaction (CO2 + H2 → CO + H2O). For over a century, these reaction mechanisms have been a central research issue in catalysis chemistry. Especially, the Sabatier process has recently received attention as a promising renewable energy technique, such as in powerto-gas (P2G) technology.6  \nMainly, three pathways have been suggested for the initial CO2 activation on Ni surfaces in previous studies by X-ray photoelectron spectroscopy (XPS),7−14 Fourier transform infrared (FT-IR) spectroscopy,14−17 high-resolution electron  \nenergy loss spectroscopy,7, 13 infrared-visible sum frequency generation, 12 temperature-programmed desorption and reaction spectros copies, 7 , 13 and theoretical calculations.7, 11, 13, 16, 18−23 One of the pathways is through CO2 dissociation into carbon monoxide (CO) and atomic oxygen (O) (CO2 → CO + O).8−10, 12, 14, 16, 17, 19,20 The other two pathways proceed through the reaction of CO2 and atomic hydrogen (H) on the surface to form carboxyl (COOH)7, 11, 13, 19,20 or formate (HCOO).7, 13, 15, 16 COOH is formed by O-terminal hydrogenation of CO2, while HCOO is  \n\n| Received: May 6, 2025\u003Cbr>Revised: November 8, 2025\u003Cbr>Accepted: November 13, 2025\u003Cbr>Published: November 21, 2025 | |\n| --- | --- |\n\n© 2025 The Authors. Published by American Chemical Society  \n58238  \n[https://doi.org/10.1021/acsomega.5c04196](https://doi.org/10.1021/acsomega.5c04196)  \nACS Omega 2025, 10, 58238−58249  \nformed by C-terminal hydrogenation of CO2. When COOH is formed, it is observed as CO and OH (COOH → CO + OH) due to its short lifetime on the surface.7, 11,20,23 HCOO is stable on Ni(111) and Ni(110) while observed as CO + H (HCOO → HCO → CO + H) on Ni(100).7, 16,23 HCOO has been observed as a typical intermediate species, especially on Ni nanoparticles on substrates,15, 16 and the Ni(11","cbCaibjsURQ5CxRK","https://ap.wps.com/l/cbCaibjsURQ5CxRK","pdf",7785288,12,"English","# ABSTRACT\n# INTRODUCTION\n## CO2 activation and competing mechanisms\n## XPS and spectroscopic pathways on Ni surfaces\n## Role of COOH and formate intermediates\n## Ambient-pressure X-ray photoelectron spectroscopy (APXPS) methods","[{\"question\":\"How does the gas dosage order affect CO2 hydrogenation intermediates on Ni(111)?\",\"answer\":\"On Ni(111), the intermediates depend on whether CO2 is introduced before H2 or vice versa. Introducing CO2 first at 300 K leads to CO2 dissociation, while the opposite order produces COOH formation.\"},{\"question\":\"What technique was used to observe the reaction pathways in this study?\",\"answer\":\"The study used in situ ambient-pressure X-ray photoelectron spectroscopy (APXPS) to monitor surface chemistry under a H2/CO2 mixed gas atmosphere.\"},{\"question\":\"At what temperatures does COOH formation dominate, and what additional process occurs at higher temperatures?\",\"answer\":\"COOH formation dominates above about 370–420 K depending on gas pressure. Graphitization is associated with temperatures above about 470 K.\"}]","Selecting Reaction Pathways of CO2 Hydrogenation on Ni(111) by Kinetic Hindrance Associated with the Initial Surface Conditions - Ambient-Pressure X-ray Photoelectron Spectroscopy | PDF",1790706641]