Microkinetic analysis of the CO2 effect on OCM over a La-Sr/CaO catalyst

IF 1.5 4区 化学 Q4 CHEMISTRY, PHYSICAL International Journal of Chemical Kinetics Pub Date : 2024-07-03 DOI:10.1002/kin.21746
Yonggang Cheng, Pedro S. F. Mendes, Parviz Yazdani, Joris W. Thybaut
{"title":"Microkinetic analysis of the CO2 effect on OCM over a La-Sr/CaO catalyst","authors":"Yonggang Cheng,&nbsp;Pedro S. F. Mendes,&nbsp;Parviz Yazdani,&nbsp;Joris W. Thybaut","doi":"10.1002/kin.21746","DOIUrl":null,"url":null,"abstract":"<p>Given its role as a primary side product and a potential soft oxidant in the oxidative coupling of methane (OCM), understanding the effect of CO<sub>2</sub> co-feeding on OCM emerges as a key milestone to optimize the process. To grasp the molecular impact of CO<sub>2</sub>, a mechanistic investigation over a La-Sr/CaO catalyst was carried out via microkinetic modeling. Seven catalyst descriptors with a precise physico-chemical meaning were regressed for both pure O<sub>2</sub> and CO<sub>2</sub> co-feeding in order to assess eventual structural changes induced in the catalyst by the presence of CO<sub>2</sub> in the feed. Global significance was achieved in both regressions and experimental trends were successfully reproduced by the specifically determined catalyst descriptors. CO<sub>2</sub> co-feeding is deemed responsible for generating a new active phase, for example, by converting metal oxides into (oxy-)carbonates, among others, resulting in a decrease in active site density (D<sub>16</sub>) from 10 × 10<sup>−5</sup> mol/m<sup>2</sup> to 7 × 10<sup>−5</sup> mol/m<sup>2</sup>. In the presence of the CO<sub>2</sub>-induced phase, the catalyst exhibits higher attraction for unsaturated hydrocarbons as indicated by the higher initial sticking probabilities of CH<sub>3</sub>• (D<sub>11</sub>) and C<sub>2</sub>H<sub>4</sub> (D<sub>15</sub>), which increase from 4.9 × 10<sup>−4</sup> to 8 × 10<sup>−2</sup> and from 2.1 × 10<sup>−2</sup> to 3 × 10<sup>−2</sup>, respectively. Additionally, there are also lower the overall energy barriers for the activation of hydrocarbons on the catalyst, stemming from the decrease in the H abstraction enthalpy from CH<sub>4</sub> (D<sub>1</sub>) from 14 to 6 kJ/mol. The operating conditions, in particular the O<sub>2</sub> content, are critical in distinguishing the effect of CO<sub>2</sub> co-feeding. While at typical operating conditions, CO<sub>2</sub> promotes the total oxidation of methane, in the prerequisite of reduced amount of O<sub>2</sub>, it may also act as an additional oxygen donor. This work provides molecular details on the CO<sub>2</sub> induced changes in catalyst properties but also provides unprecedent quantified insights of the reaction mechanism underlying experimental observations.</p>","PeriodicalId":13894,"journal":{"name":"International Journal of Chemical Kinetics","volume":null,"pages":null},"PeriodicalIF":1.5000,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Chemical Kinetics","FirstCategoryId":"92","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/kin.21746","RegionNum":4,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0

Abstract

Given its role as a primary side product and a potential soft oxidant in the oxidative coupling of methane (OCM), understanding the effect of CO2 co-feeding on OCM emerges as a key milestone to optimize the process. To grasp the molecular impact of CO2, a mechanistic investigation over a La-Sr/CaO catalyst was carried out via microkinetic modeling. Seven catalyst descriptors with a precise physico-chemical meaning were regressed for both pure O2 and CO2 co-feeding in order to assess eventual structural changes induced in the catalyst by the presence of CO2 in the feed. Global significance was achieved in both regressions and experimental trends were successfully reproduced by the specifically determined catalyst descriptors. CO2 co-feeding is deemed responsible for generating a new active phase, for example, by converting metal oxides into (oxy-)carbonates, among others, resulting in a decrease in active site density (D16) from 10 × 10−5 mol/m2 to 7 × 10−5 mol/m2. In the presence of the CO2-induced phase, the catalyst exhibits higher attraction for unsaturated hydrocarbons as indicated by the higher initial sticking probabilities of CH3• (D11) and C2H4 (D15), which increase from 4.9 × 10−4 to 8 × 10−2 and from 2.1 × 10−2 to 3 × 10−2, respectively. Additionally, there are also lower the overall energy barriers for the activation of hydrocarbons on the catalyst, stemming from the decrease in the H abstraction enthalpy from CH4 (D1) from 14 to 6 kJ/mol. The operating conditions, in particular the O2 content, are critical in distinguishing the effect of CO2 co-feeding. While at typical operating conditions, CO2 promotes the total oxidation of methane, in the prerequisite of reduced amount of O2, it may also act as an additional oxygen donor. This work provides molecular details on the CO2 induced changes in catalyst properties but also provides unprecedent quantified insights of the reaction mechanism underlying experimental observations.

查看原文
分享 分享
微信好友 朋友圈 QQ好友 复制链接
本刊更多论文
二氧化碳对 La-Sr/CaO 催化剂上 OCM 影响的微观动力学分析
鉴于二氧化碳在甲烷氧化偶联反应(OCM)中作为主要副产品和潜在软氧化剂的作用,了解二氧化碳共馈对 OCM 的影响成为优化工艺的关键里程碑。为了了解二氧化碳的分子影响,我们通过微动力学建模对 La-Sr/CaO 催化剂进行了机理研究。为了评估进料中二氧化碳的存在对催化剂结构造成的最终变化,对纯氧气和二氧化碳协同进料中具有精确物理化学意义的七个催化剂描述符进行了回归分析。两种回归结果都具有全局意义,而且实验趋势也成功地通过具体确定的催化剂描述符得到了再现。二氧化碳协同进料被认为是产生新活性相的原因,例如,通过将金属氧化物转化为(氧-)碳酸盐等,导致活性位点密度(D16)从 10 × 10-5 mol/m2 降至 7 × 10-5 mol/m2。在二氧化碳诱导相的存在下,催化剂对不饱和碳氢化合物表现出更高的吸引力,这表现在 CH3- (D11) 和 C2H4 (D15) 的初始粘附概率较高,分别从 4.9 × 10-4 增加到 8 × 10-2 和从 2.1 × 10-2 增加到 3 × 10-2。此外,催化剂活化碳氢化合物的总能障也有所降低,这是因为从 CH4(D1)中抽取 H 的焓从 14 kJ/mol 降至 6 kJ/mol。操作条件,尤其是 O2 含量,是区分 CO2 协同供料效果的关键。虽然在典型的操作条件下,二氧化碳会促进甲烷的完全氧化,但在氧气含量减少的前提下,二氧化碳也可以作为额外的氧供体。这项工作提供了二氧化碳诱导催化剂特性变化的分子细节,同时也对实验观察所依据的反应机理提供了前所未有的量化见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
求助全文
约1分钟内获得全文 去求助
来源期刊
CiteScore
3.30
自引率
6.70%
发文量
74
审稿时长
3 months
期刊介绍: As the leading archival journal devoted exclusively to chemical kinetics, the International Journal of Chemical Kinetics publishes original research in gas phase, condensed phase, and polymer reaction kinetics, as well as biochemical and surface kinetics. The Journal seeks to be the primary archive for careful experimental measurements of reaction kinetics, in both simple and complex systems. The Journal also presents new developments in applied theoretical kinetics and publishes large kinetic models, and the algorithms and estimates used in these models. These include methods for handling the large reaction networks important in biochemistry, catalysis, and free radical chemistry. In addition, the Journal explores such topics as the quantitative relationships between molecular structure and chemical reactivity, organic/inorganic chemistry and reaction mechanisms, and the reactive chemistry at interfaces.
期刊最新文献
Issue Information Issue Information Force training neural network potential energy surface models Issue Information Folic acid as a green inhibitor for corrosion protection of Q235 carbon steel in 3.5 wt% NaCl solution
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
现在去查看 取消
×
提示
确定
0
微信
客服QQ
Book学术公众号 扫码关注我们
反馈
×
意见反馈
请填写您的意见或建议
请填写您的手机或邮箱
已复制链接
已复制链接
快去分享给好友吧!
我知道了
×
扫码分享
扫码分享
Book学术官方微信
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术
文献互助 智能选刊 最新文献 互助须知 联系我们:info@booksci.cn
Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。
Copyright © 2023 Book学术 All rights reserved.
ghs 京公网安备 11010802042870号 京ICP备2023020795号-1