A scanning pulse reaction technique for transient analysis of the methanol-to-hydrocarbons reaction

A method of scanning pulse gas chromatography (SP-GC) suitable for time-resolved analysis of transient response of catalysts to reactant pulses is introduced. Applied to the methanol-to-hydrocarbons reaction over several zeolite-based catalysts (HZSM-5, Ca/ZSM-5 and Ga/ZSM-5), SP-GC provided quantitative information about the transient reactivity and selectivity during methanol conversion. The SP-GC analysis demonstrates substantial differences in the relative rates of hydrocarbon formation between catalysts that favor aromatic or olefin cycles of the dual cycle hydrocarbon pool mechanism. The influence of metal promoters on the main reaction pathways was highlighted with an emphasis on mechanistic aspects

Model-based evaluation and data requirements for parallel kinetic experimentation and data-driven reaction identification and optimization

Recently there has been growing interest in implementing the high-throughput approach to access the dynamics of chemical processes across different fields. With an ever-increasing amount of data catalyzed by high-throughput experimentation, the development of fully-integrated workflows becomes crucial. These workflows should combine novel experimental tools and interpretation methods to convert the data into valuable information. To design feasible data-driven workflows it is necessary to estimate the value of information and balance it with the number of experiments and resources required. Basing this kind of workflow on actual physical models appears to be a more feasible strategy as compared to data-extensive empirical statistical methods. Here we show an algorithm that constructs and evaluates kinetic models of different complexity. The algorithm facilitates the evaluation of the experimental data quality and quantity requirements needed for reliable discovery of the rates driving the corresponding chemical models. The influence of the quality and quantity of data on the obtained results was indicated by the accuracy of the estimates of the kinetic parameters. We also show that this method can be used to find correct reaction scenarios directly from simulated kinetic data with little to no overfitting. Well-fitting models for theoretical data can then be used as a proxy for optimizing the underlying chemical systems. Taking real physical effects into account, this approach goes beyond: we show that with the kinetic models one can make a direct, unbiased, quantitative connection between kinetic data and the reaction scenario

石炭の塩素化

種別:卒業論文東京帝国大学工学

Catalytic conversion of furanic compounds over Ga-modified ZSM-5 zeolites as a route to biomass-derived aromatics

Herein we report a mechanistic study of aromatization of furanics, as model compounds for cellulosic biomass, over (Ga)HZSM-5 catalysts. Applying combined gas chromatography and mass-spectrometry product analysis we were able to analyse conversion and selectivity reaction profiles with high temporal resolution. The thorough analysis of the product distribution allowed us to resolve the deoxygenation pathways of the furan molecules. We found that depending on the methyl substitution oxygen is removed either as water or COx, effecting the carbon efficiency of the process. While unsubstituted furan undergoes decarbonylation to form COx, methylated furans are deoxygenated by dehydration, resulting in a much higher carbon-efficiency. Furthermore, using in situ IR spectroscopy, we found that promotion of HZMS-5 with Ga in addition to enhanced aromatic selectivity influences the deactivation pathway leading to the preferential formation of proton-deficient polycyclic aromatic compounds

Aromatization of ethylene over zeolite-based catalysts

Light aromatic compounds (BTX: benzene, toluene and xylenes) represent an important class of building blocks in the chemical industry. Currently, light aromatics are obtained exclusively from fossil feedstock, whose utilization is associated with serious environmental concerns. Developing new routes for a more sustainable BTX production is, therefore, of high importance. In this work, aromatization of ethylene over well-defined metal-modified HZSM-5 zeolite catalysts is examined. The results show that modification of zeolite with gallium, zinc and silver leads to a significant increase in aromatics production. Metal species are responsible for catalysing dehydrogenation pathways with Ga being the most efficient for BTX production. Increasing temperature and ethylene partial pressure facilitate ethylene aromatization. Employing a combination of isotope labelling with a thorough characterization of zeolite-entrapped species by means of IR and MAS NMR spectroscopy provides evidence for the involvement of intra-zeolite aromatic hydrocarbon species in the catalytic cycle

Tuning the reactivity of molybdenum (oxy)carbide catalysts by the carburization degree: CO2 reduction and anisole hydrodeoxygenation

Molybdenum (oxy)carbide catalysts supported on activated carbon were prepared by a carbothermal hydrogen reduction method without passivation step. Four carburization temperatures (500 °C, 600 °C, 700 °C and 800 °C) were selected to control the catalyst carburization degree based on studies of catalyst precursor carburization process by TGA-MS and in situ XANES. Quasi in situ XRD, XAS and XPS revealed that two types of material were produced – molybdenum oxycarbide (500 °C and 600 °C) and molybdenum carbide (700 °C and 800 °C) catalysts. The oxycarbide catalysts are rich in Mo-oxide and Mo-oxycarbide species (MoO2 and MoOxCy) and the carbide catalysts rich in Mo-carbide species (α-MoC1−x and β-Mo2C) with a certain remaining oxygen atoms. The carbidic and oxophilic Mo sites in the catalysts were respectively probed by CO and N2O chemisorption. The structure–performance relationships of these catalysts in CO2 hydrogenation and anisole hydrodeoxygenation (HDO) were studied. For CO2 hydrogenation, the carbide catalysts were much active than the oxycarbide catalysts and CO was the main product in all the catalysts. In contrast, the oxycarbide and carbide catalysts displayed comparable activity towards anisole conversion and the main products shifted from a mixture of phenol and benzene to only benzene upon increasing the carburization temperature from 600 °C to 700 °C. These catalytic results demonstrate that the catalytic performance of molybdenum (oxy)carbide material can be effectively tuned by varying the carburization degree and such tuning effect depends on the nature of reactant molecules: the carbidic Mo sites in Mo-carbide species are associated with CO2 and anisole-to-benzene conversions, and the oxophilic Mo sites in Mo-oxycarbide species are related to anisole-to-phenol conversion

Catalytic conversion of furanic compounds over Ga-modified ZSM-5 zeolites as a route to biomass-derived aromatics

\u3cp\u3eHerein we report a mechanistic study of aromatization of furanics, as model compounds for cellulosic biomass, over (Ga)HZSM-5 catalysts. Applying combined gas chromatography and mass-spectrometry product analysis we were able to analyse conversion and selectivity reaction profiles with high temporal resolution. The thorough analysis of the product distribution allowed us to resolve the deoxygenation pathways of the furan molecules. We found that depending on the methyl substitution oxygen is removed either as water or CO\u3csub\u3ex\u3c/sub\u3e, effecting the carbon efficiency of the process. While unsubstituted furan undergoes decarbonylation to form CO\u3csub\u3ex\u3c/sub\u3e, methylated furans are deoxygenated by dehydration, resulting in a much higher carbon-efficiency. Furthermore, using in situ IR spectroscopy, we found that promotion of HZMS-5 with Ga in addition to enhanced aromatic selectivity influences the deactivation pathway leading to the preferential formation of proton-deficient polycyclic aromatic compounds.\u3c/p\u3

Basic Promotors Impact Thermodynamics and Catalyst Speciation in Homogeneous Carbonyl Hydrogenation

Homogeneously catalyzed reactions often make use of additives and promotors that affect reactivity patterns and improve catalytic performance. While the role of reaction promotors is often discussed in view of their chemical reactivity, we demonstrate that they can be involved in catalysis indirectly. In particular, we demonstrate that promotors can adjust the thermodynamics of key transformations in homogeneous hydrogenation catalysis and enable reactions that would be unfavorable otherwise. We identified this phenomenon in a set of well-established and new Mn pincer catalysts that suffer from persistent product inhibition in ester hydrogenation. Although alkoxide base additives do not directly participate in inhibitory transformations, they can affect the equilibrium constants of these processes. Experimentally, we confirm that by varying the base promotor concentration one can control catalyst speciation and inflict substantial changes to the standard free energies of the key steps in the catalytic cycle. Despite the fact that the latter are universally assumed to be constant, we demonstrate that reaction thermodynamics and catalyst state are subject to external control. These results suggest that reaction promotors can be viewed as an integral component of the reaction medium, on its own capable of improving the catalytic performance and reshaping the seemingly rigid thermodynamic landscape of the catalytic transformation

Different mechanisms of ethane aromatization over Mo/ZSM-5 and Ga/ZSM-5 catalysts

Aromatization of light hydrocarbons can contribute to a secure supply of aromatics for the chemical industry. In this work, we investigate the influence of modification of zeolite ZSM-5 with Ga and Mo on the reaction mechanism underlying the activation and aromatization of ethane. Well-defined Mo/ZSM-5 and Ga/ZSM-5 zeolites efficiently promote ethane aromatization to benzene-toluene-xylene mixtures. Both catalysts suffer from coke formation, which leads to rapid deactivation. From catalytic tests, temperature-programmed surface reaction and pulsed reaction experiments, we infer that ethane conversion on Ga/ZSM-5 follows a conventional sequential dehydrogenation-oligomerization-aromatization mechanism, while the reaction over Mo/ZSM-5 involves reactive surface carbon (hydrocarbon pool) species

Reversible nature of coke formation on Mo/ZSM-5 methane dehydroaromatization catalysts

Non-oxidative dehydroaromatization of methane over Mo/ZSM-5 zeolite catalysts is a promising reaction for the direct conversion of abundant natural gas into liquid aromatics. Rapid coking deactivation hinders the practical implementation of this technology. Herein, we show that catalyst productivity can be improved by nearly an order of magnitude by raising the reaction pressure to 15 bar. The beneficial effect of pressure was found for different Mo/ZSM-5 catalysts and a wide range of reaction temperatures and space velocities. High-pressure operando X-ray absorption spectroscopy demonstrated that the structure of the active Mo-phase was not affected by operation at elevated pressure. Isotope labeling experiments, supported by mass-spectrometry and 13 C nuclear magnetic resonance spectroscopy, indicated the reversible nature of coke formation. The improved performance can be attributed to faster coke hydrogenation at increased pressure, overall resulting in a lower coke selectivity and better utilization of the zeolite micropore space