| C1 chemistry is the conversion of one-carbon molecules into chemicals with high economic and industrial value.However,the research on the related catalytic mechanism is limited by the reaction conditions required and research equipment capable of meeting this requirement.Thus it is difficult to implement a rational design of a catalyst for such processes with the current limitations.The work presented here focuses on the application of in situcharacterization platform based on online mass spectrometry(MS)in the field of C1 mechanistic study and focusing on the design and building of an in situ characterization platform with online MS as the core analytical tool.The advantage of this in situ characterization platform allows for multi-characterization and multi-purpose capability.Two main directions were studied using a platform-based online MS microreactor.Firstly,a method for measuring the chemical specific surface area of the metal cluster supported by the active carrier by low-temperature chemical titration was developed for the metal supported catalysts,demonstrating with catalysts such as Pt/Fe2O3and Cu/CeO2.The mechanism of CO oxidation on Au/TiO2 was also studied.In addition,the product kinetics of the methane oxidative coupling(OCM)reaction on the nanorod La2O3 catalyst and the formation mechanism of the catalytic active surface in the reaction were investigated.The introduction introduces the main reactions of C1 chemistry,the concept of supported catalyst,the importance of studying the mechanism of catalytic reaction,the difficulties and limitations of the mechanism research,the basic working principle and development history of common surface research instruments,and the definition and importance of in situ and operandocharacterization.Thus it is necessary to design and develop characterization equipment and methods that meet the requirements for catalyst characterization and reaction mechanism with respect to the catalyst.The second chapter details the design and construction of the online and in situ mass spectrometry(MS)platform.The complete platform is divided between:An online micro-reactor setup that is coupled to online MS for fast time resolved gas detection,In situ XPS,In situ XRD apparatus,In situ FTIR.The advantages of this online MS sampling platform is that it can be used in high pressure and a wide temperature range(liquid nitrogen temperatures to 800°C)and having high sensitivity and fast time response gas detection.This is followed by the application of the in situ characterization platform through the following key studies:1.Characterization techniques by using dynamic chemisorption to characterize catalyst active sites.This involves the characterization of the supported Pt and Cu catalysts,probed using CO oxidation and N2O decomposition respectively,and conducted using low-temperature titration.2.Investigation towards the reaction mechanism of CO oxidation on Au/TiO2.3.The study of Oxidative Coupling of Methane(OCM)reaction using La2O3, focusing on the reaction kinetics4.Exploration of OCM reaction mechanism over La2O3.In this work,chemisorption characterization is performed for supported metal catalysts.Using online micro-reactor MS system,a low-temperature titration technique is employed to determine the surface area of metal sites on supported catalysts.In this work,application of this technique over known catalysts is shown,demonstrating with CO and N2O as probe molecules and used to titrate Pt and Cu nanoparticles respectively.The metal particle surface area,dispersion and particle size of the particles can be determined using this technique.After demonstration of the titration technique,this method can be further applied to the characterization of complex active sites of catalysts.This is extended to the study of the CO oxidation mechanism on Au/TiO2.In the real application of the online MS platform,CO oxidation experiments were carried out on Au/TiO2catalyst,A variety of experimental techniques is employed,focusing on CO-TPD,steady state isothermal titration,Temperature Programmed Reduction(TPR),and low temperature selective Temperature Programmed Oxidation(TPO)experiments.In this work,it is shown that CO-TPD revealed the presence of two different CO species adsorbed on the Au/TiO2surface.Steady state isothermal titrations showed two transient processes that demonstrated different redox sequences.High temperature CO titration transients with 200°C pre-oxidation following either isothermal CO titration or high temperature TPR highlights the presence of two oxidative surface intermediate species with different kinetics.Finally,low temperature selective TPO beginning at 165°C showed that pre-reduction following oxidation up to 100°C is able to partially convert surface CO species into stable CO2intermediates.The OCM reaction is a reaction that directly converts CH4 into C2 species.However the main disadvantages of the reactions its low selectivity towards C2 products forming mainly COx product,and complex side reactions that can occur.By performing OCM over a nanorod La2O3 catalyst and analyzed using a combination of the in situ characterization and the online MS platform.It is found that OCM light-off occurs between 500-650~oC,denoted as the turnover zone.It is also found that once COx formation reaches a maximum,C2 selectivity increases and as a result sees the activation energy become decreased.In order to study the formation conditions of the catalytic active surface,the adsorption and desorption characteristics of O2 on La2O3 catalyst were studied by different treatments of the catalyst,whereby the steps of OCM reaction elements were studied using CH4 titration and TPR experiments,introducing CH4 at different temperatures of the oxidized La2O3 surface.The work found that the bulk phase carbonate species generated after the reaction gas treatment could poison the catalyst.It was also observed that the surface of the catalyst still contains active species even in the absence of oxygen,suggesting that C2products can be generated at high temperature.The results demonstrated also that this active site could still exist stably after the cooling and heating process.The work presented here has laid a good foundation for the follow-up work.In the future research work,in situ XRD-MS can be used to study the phase structure change of the La2O3 catalyst during the reaction process and establish the relationship between carbonate species and catalyst activity.It is also necessary to use XPS-MS to study the species and electronic structure of surface in order to better understand the nature of the active species on the catalyst surface.This present work provides vital information towards understanding OCM. |
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