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The aim of this PhD thesis is to design new catalytic materials for the CH4 oxychlorination (MOC) reaction and to study these solid catalysts under real working conditions by applying light, i.e., operando spectroscopy. In this way, the activity and spectroscopic information can be coupled, yielding crucial mechanistic insights to improve the design of the catalytic materials. The presented work reveals that redox properties, bulk and synergistic effects play a crucial role in the working mechanism of bulk MOC catalysts. In chapter 2, a set of lanthanide oxychloride catalysts were synthesized, characterized and tested. EuOCl came out as the most promising candidate as it possessed the highest MOC activity, the best activity/selectivity relation and was proven to be stable. Moreover, the catalytic performance of EuOCl could be tuned by increasing the HCl concentration in the feed, thereby mitigating the unwanted catalytic destruction of chloromethanes to COx. Operando Raman spectroscopy revealed that the chlorination of the catalyst was rate limiting as an increase in the HCl concentration in the feed resulted in enhancement of activity, but did not cause bulk chlorination of the catalyst. While EuOCl appeared promising as a MOC catalyst, its catalytic performance was limited by the rate of chlorination. The catalyst design was improved in chapter 3 by adding a chlorinating agent for Eu3+. The activity of all La3+-Eu3+ bimetallic catalysts was significantly higher than anticipated for the linear combination of LaOCl and EuOCl. More important was that a higher CH3Cl selectivity could be achieved without giving in on the excellent CO selectivity obtained for monometallic EuOCl. Operando luminescence spectroscopy revealed that La3+ acted as a chlorinating agent for Eu3+, even when the phases were completely segregated as in the case for the physical mixture. By applying operando catalyst thermometry in chapter 4, the observed catalytic performance of EuOCl could be linked to the actual catalyst temperature, gaining more insights in arguably one of the most important reaction parameters. A catalyst temperature of maximum 16 °C higher compared to the oven temperature was recorded, due to the exothermic nature of the MOC reaction. Heat dissipation by means of radiation was identified as the main heat loss mechanism, resulting in a uniform catalyst bed temperature. The concept that irreducible elements can make up a very active catalyst for the MOC reaction is proven by the design of irreducible Mg2+-Al3+ mixed-metal oxide (MMO) catalysts. The Mg4Al MMO possessed one of the highest reported activities under the tested reaction conditions, which was all the more surprising considering that MgO and -Al2O3 did not show any significant activity. Operando Raman spectroscopy revealed that Mg2+ acted as a Cl- buffer and as a chlorinating agent for Al3+, which was the active metal in the CH4 activation step. Adding 2 atom-% of the redox active Eu3+ in the material doubled the activity, made the activity/selectivity relation tuneable and preserved the activity under high HCl concentrations. These results indicate that both redox activity as well as synergistic effects are required to obtaining benchmark performance.

The aim of this PhD thesis is to design new catalytic materials for the CH4 oxychlorination (MOC) reaction and to study these solid catalysts under real working conditions by applying light, i.e., operando spectroscopy. In this way, the activity and spectroscopic information can be coupled, yielding crucial mechanistic insights to improve the design of the catalytic materials. The presented work reveals that redox properties, bulk and synergistic effects play a crucial role in the working mechanism of bulk MOC catalysts. In chapter 2, a set of lanthanide oxychloride catalysts were synthesized, characterized and tested. EuOCl came out as the most promising candidate as it possessed the highest MOC activity, the best activity/selectivity relation and was proven to be stable. Moreover, the catalytic performance of EuOCl could be tuned by increasing the HCl concentration in the feed, thereby mitigating the unwanted catalytic destruction of chloromethanes to COx. Operando Raman spectroscopy revealed that the chlorination of the catalyst was rate limiting as an increase in the HCl concentration in the feed resulted in enhancement of activity, but did not cause bulk chlorination of the catalyst. While EuOCl appeared promising as a MOC catalyst, its catalytic performance was limited by the rate of chlorination. The catalyst design was improved in chapter 3 by adding a chlorinating agent for Eu3+. The activity of all La3+-Eu3+ bimetallic catalysts was significantly higher than anticipated for the linear combination of LaOCl and EuOCl. More important was that a higher CH3Cl selectivity could be achieved without giving in on the excellent CO selectivity obtained for monometallic EuOCl. Operando luminescence spectroscopy revealed that La3+ acted as a chlorinating agent for Eu3+, even when the phases were completely segregated as in the case for the physical mixture. By applying operando catalyst thermometry in chapter 4, the observed catalytic performance of EuOCl could be linked to the actual catalyst temperature, gaining more insights in arguably one of the most important reaction parameters. A catalyst temperature of maximum 16 °C higher compared to the oven temperature was recorded, due to the exothermic nature of the MOC reaction. Heat dissipation by means of radiation was identified as the main heat loss mechanism, resulting in a uniform catalyst bed temperature. The concept that irreducible elements can make up a very active catalyst for the MOC reaction is proven by the design of irreducible Mg2+-Al3+ mixed-metal oxide (MMO) catalysts. The Mg4Al MMO possessed one of the highest reported activities under the tested reaction conditions, which was all the more surprising considering that MgO and -Al2O3 did not show any significant activity. Operando Raman spectroscopy revealed that Mg2+ acted as a Cl- buffer and as a chlorinating agent for Al3+, which was the active metal in the CH4 activation step. Adding 2 atom-% of the redox active Eu3+ in the material doubled the activity, made the activity/selectivity relation tuneable and preserved the activity under high HCl concentrations. These results indicate that both redox activity as well as synergistic effects are required to obtaining benchmark performance.

The use of ethane as a platform molecule for the manufacture of polyvinyl chloride (PVC) is a longstanding challenge, which would allow to reduce the raw material costs and CO2 emissions to produce this plastic. Herein, we discover that rare earth oxychlorides catalyze in a selective (up to 90 %) and stable (>50 h on stream) manner the reaction of ethane and molecular chlorine into 1,2-dichloroethane, which, upon established cracking, will translate into an order of magnitude higher vinyl chloride productivity compared to ethane oxychlorination technologies. In addition, representative europium oxychloride was supported on suitable carriers and was demonstrated to be selective (up to 90 %) and stable (>40 h on stream) in extrudate form. These findings bring the ethane-based production of PVC one step closer to implementation. © 2021 Wiley-VCH GmbH, Angewandte Chemie. International Edition, 60 (45), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Commercialization of CH4 valorization processes is currently hampered by the lack of suitable catalysts, which should be active, selective, and stable. CH4 oxychlorination is one of the promising routes to directly functionalize CH4, and lanthanide-based catalysts show great potential for this reaction, although relatively little is known about their functioning. In this work, a set of lanthanide oxychlorides (i.e., LnOCl with Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho) and Er- and Yb-based catalysts were synthesized, characterized, and tested. All lanthanide-based catalysts can directly activate CH4 into chloromethanes, but their catalytic properties differ significantly. EuOCl shows the most promising catalytic activity and selectivity, as very high conversion levels (>30%) and chloromethane selectivity values (>50%) can be reached at moderate reaction temperatures (∼425 °C). Operando Raman spectroscopy revealed that the chlorination of the EuOCl catalyst surface is rate-limiting; hence, increasing the HCl concentration improves the catalytic performance. The CO selectivity could be suppressed from 30 to 15%, while the CH4 conversion more than doubled from 11 to 24%, solely by increasing the HCl concentration from 10 to 60% at 450 °C. Even though more catalysts reported in this study and in the literature show a negative correlation between the S CO and HCl concentration, this effect was never as substantial as observed for EuOCl. EuOCl has promising properties to bring the oxychlorination one step closer to an economically viable CH4 valorization process.

Monitoring and simulating the events occurring on the catalysts under the real reaction conditions has significant meaning for elucidating the dynamic changes of the active sites during the reactio...

During the production of ethylene dichloride, the entrainment of catalyst particles out of the bed is considered a problematic issue that affects the conversion of the hydrogen dichloride and causes repeated unit shut down. In this study the effect of the various operating conditions was measured; the fluidizing gas flowrate, the bed parameters, the reaction conditions, and the static design parameters such as the internal orifice diameter of the distributer. A simulation model was built using Mat Lab and Aspen Plus software. The results from both models were compared with the sample analysis data obtained from the laboratory. It was found that when the entering gas flow rate reached 2570.4 m3/hr, the bubble diameter of the fluidizing gas reached maximum value, and hence, the entrainment of catalyst particles was at the lowest quantity of about 8.2 Kg/m2.s. In addition, it was found that as the pressure drop through the orifice of the distributer decrease the entrainment of solids increase until an orifice diameter of 1 cm is reached, hence, the lowest rate of entrainment of catalyst particles is achieved. at such conditions the highest conversion of ethylene and HCL into Ethylene dichloride could be reached.

The direct conversion of CH 4 into fuels and chemicals produces less waste, requires smaller capital investments, and has improved energy efficiency compared to multistep processes. While the methane oxychlorination (MOC) reaction has been given little attention, it offers the potential to achieve high CH 4 conversion levels at high selectivities. In a continuing effort to design commercially interesting MOC catalysts, we have improved the catalyst design of EuOCl by the partial replacement of Eu 3+ by La 3+. A set of catalytic solid solutions of La 3+ and Eu 3+ (i.e., La x Eu 1- x OCl, where x = 0, 0.25, 0.50, 0.75, and 1) were synthesized and tested in the MOC reaction. The La 3+-Eu 3+ catalysts exhibit an increased CH 3Cl selectivity (i.e., 54-66 vs 41-52%), a lower CH 2Cl 2 selectivity (i.e., 8-24 vs 18-34%), and a comparable CO selectivity (i.e., 11-28 vs 14-28%) compared to EuOCl under the same reaction conditions and varying HCl concentrations in the feed. The La 3+-Eu 3+ catalysts possessed a higher CH 4 conversion rate than when the individual activities of LaOCl and EuOCl are summed with a similar La 3+/Eu 3+ ratio (i.e., the linear combination). In the solid solution, La 3+ is readily chlorinated and acts as a chlorine buffer that can transfer chlorine to the active Eu 3+ phase, thereby enhancing the activity. The improved catalyst design enhances the CH 3Cl yield and selectivity and reduces the catalyst cost and the separation cost of the unreacted HCl. These results showcase that, by matching intrinsic material properties, catalyst design can be altered to overcome reaction bottlenecks.

Ethylene oxychlorination is the key technology in vinyl chloride (VCM, the monomer of PVC, polyvinyl chloride) production to close the chlorine loop by consuming the HCl released from the former cracking step. Due to the high demand for PVC, this leads to ethylene oxychlorination being one of the most important processes in the industry. This Review covers an in-depth analysis of the dynamic nature of active sites for the main and side reactions involved in ethylene oxychlorination, featuring the findings and viewpoints from the dynamic kinetics study and analysis under industrial operating conditions. A unified picture of the mechanism of the surface reactions, and the effect of supports and promoters, has been presented based on the decoupled redox-cycle experiments, which leads to a significantly better understanding of the mechanism and provides valuable guidelines for effective catalyst design. Operando techniques and kinetic tools of the rate-diagram, as well as their application to the study of the redox-cycle in ethylene oxychlorination and kinetic models on both the main product and byproduct, are also reviewed. Perspectives on challenges and new process development and future research focus for better study of the VCM production chemistry are also proposed. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

Identifying surface-active sites and reaction pathways is of great significance in heterogeneous catalysis. However, even for the simplest catalytic reaction, there could exist a myriad of possible...

A dual system comprising two catalytic reactors connected in series was developed for the direct conversion of ethene to vinyl chloride monomer (VCM). The first reactor uses ZrO2-supported ceria (CeO2/ZrO2) to perform ethene oxychlorination to 1,2-dichloroethene (EDC) that is dehydrochlorinated to VCM in the second reactor over calcium-promoted γ-Al2O3. The choice of carrier for ceria is of critical importance to maximize the EDC production by reducing combustion products. While MgO, SiO2, SiC, TiO2, ZSM-5, and γ-Al2O3 carriers induced higher overoxidation compared to bulk ceria, ZrO2 was the only carrier that suppressed COx formation. Moreover, the latter carrier led to the highest oxychlorination activity. The unique performance of the CeO2/ZrO2 catalyst was rationalized by its ability to promote chlorine evolution and to suppress the combustion of chlorinated products, as inferred from the activity evaluation in HCl and VCM oxidation, respectively. The outstanding redox properties, enabling operation at low temperature and thus high selectivity, are associated with the formation of defective CeO2 nanoparticles, contrasting the low activity over Ce–Zr mixed oxide. In order to subsequently form VCM, an efficient EDC dehydrochlorination catalyst was designed by moderating the acidity of γ-Al2O3via calcium doping and used in a reactor after CeO2/ZrO2. This dual catalyst system displayed 100% selectivity to VCM at 25% ethene conversion, surpassing the space time yield of the best ethene-to-VCM catalyst EuOCl by a factor of four, where the first step is operated at an elevated temperature of about 100–150 K with respect to cupric chloride benchmarks. In addition, the catalytic dehydrochlorination, operated at a lower temperature of 100 K than the current non-catalytic process, showed minimized coke formation. This developed system rendered stable after slight initial deactivation, offering promising potential to intensify VCM production.

High partial oxidation selectivity in ethylene oxidation over Ag catalysts is achieved in part via the presence of adsorbed chlorine promoters. Chlorine coverage during ethylene oxidation is maintained by co-feeding organic chlorides in ppm levels and alkane moderators in concentrations of ~0.5 mol%. The relative efficacy of organic chlorides in Cl deposition and of alkanes in Cl removal is typically estimated using empirical correlations. Apparent kinetics of Cl removal were measured by feeding ethyl chloride and propane during ethylene oxidation catalysis over a highly-promoted Ag/α-Al2O3 catalyst and quantifying the rate of chloropropane formation during steady state reaction. Propane oxychlorination forms 1- and 2-chloropropane in a ~1:2 ratio, as expected given the lower bond dissociation enthalpy of methylene than methyl C H bonds in propane, and at total rates on the order of 10-4 mol C3H7Cl (mol Agsurf)-1 s−1. Concurrent ethylene oxidation rates of order 10-1 mol (mol Agsurf)-1 s−1 provide evidence that Cl moderation occurs in a distinct catalytic cycle over promoted Ag catalysts. Cl removal has a supralinear dependence on propane pressure (PC3H8) and an inverse dependence on ethyl chloride pressure (PC2H5Cl) at high PC2H5Cl/PC3H8, while Cl removal is positive order in pressures of both C2H5Cl and C3H8 at low PC2H5Cl/PC3H8, as expected for surfaces that are increasingly covered in Cl as PC2H5Cl/PC3H8 increases. Chloropropane formation rates were positive order in dioxygen pressure for all PC2H5Cl/PC3H8 ratios. Taken together, the kinetics of Cl removal require both rate determining deposition of Cl from an alkyl chloride and kinetically relevant removal of Cl by an alkane. We develop a kinetic model that describes these trends and allows for quantification of rate and equilibrium parameters, and provide evidence for the elementary steps enumerated by measuring a kinetic isotope effect and assessing the fate of alkyl fragments from chloroethane and chloropropane in gas-phase batch reactions. Rate and equilibrium constants regressed from this kinetic model are used to develop an isotherm for Cl coverage as a function of the ratio of organic chloride promoter to alkane moderator pressures. This isotherm quantitatively predicts Cl coverages measured in situ after steady state reactions with feedstreams containing both ethyl chloride-ethane and ethyl chloride-propane mixtures. Measured reaction orders for chloropropane formation with respect to ethylene and carbon dioxide pressure reflect surface ethylene and carbon dioxide coverages that are lower for sites that form chloropropane than for sites that form ethylene oxide, suggesting that site ensembles for Cl deposition and removal vary from those involved in selective oxidation of ethylene.

An amorphous ZrO2 mesoporous material was prepared by propylene oxide (PO)-assisted sol-gel process and was first evaluated in CH4 oxychlorination. Various characterizations were conducted including XRD, N2 adsorption–desorption, NH3-TPD, CO2-TPD, SEM, and TEM. Results showed the amorphous ZrO2 with mesoporosity and large SSA exhibited abundant surface acid and base sites. As a non-redox catalyst, the amorphous ZrO2 unexpectedly delivered much higher activity and better stability in CH4 oxychlorination than conventional ZrO2. The CH4 conversion was 18.6% and the selectivity of CH3Cl and CO reached 47.6% and 30.2% at 490 °C, respectively. The amorphous ZrO2 could stably operate at 470 °C for 50 h without significant deactivation. Kinetic studies revealed that the CH4 activation on the surface of the amorphous ZrO2 was the rate-determining step.

This article investigates phosphates of transition metals (MPO, M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) as catalysts for the selective transformation of propane via oxychlorination chemistry to prop...

A series of novel spinel oxide catalysts, Cu1−xMgxCr2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1), for the ethane oxychlorination catalytic reaction were prepared by a sol–gel method, and X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller, H2 temperature-programmed reduction, O2 temperature-programmed desorption, and X-ray photoelectron spectroscopy were used to characterize the catalysts. It was found that the enhanced catalytic performance could be attributed to A-site doping of Mg2+ in the CuCr2O4 catalysts. The addition of Mg2+ changes the preferred orientation of the crystal from CuCr2O4 (0 2 0) to Cu0.6Mg0.4Cr2O4 (1 2 1) and leads to lattice distortions and more surface defect oxygen species in Cu0.6Mg0.4Cr2O4. The Cu0.6Mg0.4Cr2O4 catalyst shows optical catalytic performance for ethane oxychlorination, with an average ethane conversion of 95.6% and a vinyl chloride selectivity of 50.2%. Density functional theory results showed that the Cu0.6Mg0.4Cr2O4 catalyst would enhance the adsorption ability of the crystal (1 2 1) plane for C2H6, C2H3Cl, and C2H4. C2H3Cl is preferentially desorbed in the conversion of reactant C2H6 on the (1 2 1) plane. It is evident that the difference in electron density between C2H3Cl and C2H4 on the planes contributes to the improvement of Cu0.6Mg0.4Cr2O4 selectivity.

The product distribution in direct alkane functionalization by oxyhalogenation strongly depends on the halogen of choice. We demonstrate that the superior selectivity to olefins over an iron phosphate catalyst in oxychlorination is the consequence of a surface‐confined reaction. By contrast, in oxybromination alkane activation follows a gas‐phase radical‐chain mechanism and yields a mixture of alkyl bromide, cracking, and combustion products. Surface‐coverage analysis of the catalyst and identification of gas‐phase radicals in operando mode are correlated to the catalytic performance by a multi‐technique approach, which combines kinetic studies with advanced characterization techniques such as prompt‐gamma activation analysis and photoelectron photoion coincidence spectroscopy. Rationalization of gas‐phase and surface contributions by density functional theory reveals that the molecular level effects of chlorine are pivotal in determining the stark selectivity differences. These results provide strategies for unraveling detailed mechanisms within complex reaction networks.

Oxychlorination of ethene was conducted in a microreactor (150–375 °C) over a thin layer of CeO2 prepared in the current work with the specific surface area of 80 m2/g and compared with the same reaction in millireactors (250–500 °C). The kinetic analysis revealed influence of the ethene concentration on the apparent activation energy which was different in micro- and millireactors. The previously developed reaction network was completed by including two parallel reactions for formation of ethylchloride and vinylchloride and two consecutive reactions accounting for formation of dichloroethane and vinylchloride via ethyl chloride. The reaction orders with respect to HCl and O2 in the microreactor were comparable with the literature data for millireactors. Kinetic modeling was successfully carried for all reactants by using a steady state model of a packed bed reactor.

Through exploring the impact of dichloromethane on the chloromethane to olefins reaction, it is shown in this paper that a small amount of dichloromethane in the chloromethane feed has a drastically negative impact on the performance of SAPO-34 catalyst for the chloromethane to olefins reaction. Such impact on the catalyst performance is due to dichloromethane reacting with hydroxyl groups on the catalyst surface through a reaction that produces chloromethane. Based on this learning, we show that dichloromethane can be converted to chloromethane while performing the methane oxychlorination reaction using a layered catalyst bed approach by placing a bed of γ-Al2O3 catalyst below a CeO2 oxychlorination catalyst. Our results were successful in showing that a layered catalyst design using γ-Al2O3 as catalyst is an effective means of eliminating dichloromethane from the oxylchorination product stream and simultaneously providing an uplift to the chloromethane production rate. Such approach can serve as a one-step selective monochlorination route for production of chloromethane from methane.

This article investigates SiO2-supported Ru-, Pt-, Ir-, Rh-, and Pd-based catalysts (1 wt % metal loading) as new catalytic systems for the oxychlorination and oxybromination of methane, both pivotal steps in the halogen-mediated production of commodities from natural gas. Furthermore, this article provides insights into the structure–performance relationships and mechanism of these reactions as a function of the metal and the hydrogen halide. In-depth characterization of the equilibrated catalysts by X-ray diffraction, electron microscopy, Raman, and X-ray photoelectron spectroscopies demonstrate a fast restructuring of the starting oxide nanoparticles into metallic, metal silicide, or metal halide phases. The oxychlorination activity, which decreases in the order: Ru/SiO2 > Pt/SiO2 > Ir/SiO2 > Rh/SiO2 ≈ Pd/SiO2, is enhanced in the presence of metal oxides, while the activity order in oxybromination: Ru/SiO2 ≈ Ir/SiO2 ≈ Pd/SiO2 > Pt/SiO2 > Rh/SiO2 is less dependent on the phase composition. The highest s...

Optimal ethylene oxide selectivity during steady-state ethylene oxidation over Cs and Re-promoted Ag/α-Al2O3 catalysts is attained only if co-fed alkyl chlorides deposit chlorine adatoms and co-fed alkanes moderate surface chlorine coverages. Surface chlorine coverage under reaction conditions was measured in chemical transient studies immediately after reaching steady-state by removing reactants in flowing helium and recirculating ethane and oxygen in a gas-phase batch reactor; this resulted in removal of chlorine from the catalyst as ethyl chloride and enabled assessment of the total number of moles of chlorine desorbed per surface silver atom, which varied from 0.10 to 0.45 depending on the process conditions employed. Batch recirculation experiments demonstrated that oxygen is required to remove chlorine from silver catalysts, suggesting molecular events akin to those involved in oxychlorination of alkanes moderate chlorine coverage during steady-state catalysis. The chlorine content was largely unperturbed by changes in ethylene (20–40 mol%), carbon dioxide (1–5%), or oxygen (2–7%) concentrations during steady-state catalysis. Increasing temperature resulted in a monotonic decrease in chlorine coverage. A power law model accurately describes trends in chlorine coverage as a function of steady-state ethane (0.1–15 mol%) or ethyl chloride (0.5–6.3 ppmv) concentrations. The carbon selectivity for ethylene oxide increases with chlorine coverage, in agreement with expectations from steady-state measurement of rates and selectivity as a function of co-fed alkyl chloride promoters. These results explicate the critical role of oxygen-containing species in moderating Cl coverage during ethylene epoxidation catalysis, include a model that describes chlorine coverage across a broad concentration range of alkyl chloride promoter and alkane moderators, and enable correlation between kinetic parameters measured as a function of process conditions and the predicted chlorine coverage.

Anti-sintering platinum-based catalyst for propane dehydrogenation (PDH) is promising to avoid corrosive oxychlorination re-dispersion of sintered Pt during coke combustion. Herein, we report an anti-sintering Pt/MgAl2O4 catalyst and optimizations on its activity for PDH with group IB metals (Cu, Ag and Au). Using a suite of characterizations including BET, H2 chemisorption, XRD, STEM, CO-DRIFTs, XANES, XPS, TG/DTA, TPO, C3H6-TPD and TPSR of C3H6 with H2, we reveal that Cu and Ag dilute the surface Pt atoms and donate electron to Pt while the case for Pt-Au is inverse. As a result, significant enhancements in propane conversion and propylene selectivity were obtained on the Pt-Cu/MgAl2O4 and Pt-Ag/MgAl2O4 catalysts. The Pt-Cu/MgAl2O4 exhibited excellent C3H6 yield and regeneration stability, presumably due to the formation of intermetallic compounds and little phase segregation during cyclic dehydrogenation-regeneration runs.

Methane activation through oxychlorination is in the spotlight due to the relatively mild reaction conditions at atmospheric pressure and in the temperature range of 450–550 °C. Although CO2 is known to exhibit good activity for methane oxychlorination, significant amounts of by-products such as CO2, CO and carbon deposits are produced during the reaction over CO2. We investigated the effect of iron in FeOx/CO2 catalysts on methane oxychlorination. FeOx/CO2 with 3 wt% iron shows the maximum yield at 510 °C with 23% conversion of methane and 65% selectivity of chloromethane. XRD and H2 TPR results indicate that iron-cerium solid solution was formed, resulting in the production of more easily reduced cerium oxide and the suppression of catalysts sintering during the reaction. Furthermore, the selectivity of by-products decreased more significantly over FeOx/CO2 than cerium oxide, which can be attributed to the facilitation of HCl oxidation arising from the enhanced reducibility of the former sample.

Identification and quantification of redox‐active centers at relevant conditions for catalysis is pivotal to understand reaction mechanisms and requires development of advanced operando methods. Herein, we demonstrate operando EPR spectroscopy as an important technique to quantify the oxidation state of representative CrPO4 and EuOCl catalysts during propane oxychlorination, an attractive route for propylene production. In particular, we show for the first time that the space‐time‐yield of C3H6 correlates with the amount of Cr2+ and Eu2+ ions generated over the catalysts during reaction. These results provide a powerful strategy to gather quantitative understanding of selective alkane oxidation, which could potentially be extrapolated to other functionalization approaches and operating conditions. © 2020 Wiley‐VCH GmbH., Angewandte Chemie. International Edition, 60 (7), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

In this chapter, two industrial processes of gas-phase, hydrocarbon catalytic oxidation are examined: (a) the oxychlorination of ethylene to 1,2-dichloroethane; and (b) the oxidation of n-butane to maleic anhydride. In the former case, the use of ethane as an alternative reactant has been studied, still without success, whereas in the latter case the alkane has replaced the corresponding C4 alkenes because of the better selectivity achieved. Recent developments are discussed for the two reactions, especially in terms of catalysts’ chemical-–physical and reactivity properties.