Evgenii V. Kondratenko

Status and perspectives of CO2 conversion into fuels and chemicals by catalytic, photocatalytic and electrocatalytic processes

This review highlights recent developments and future perspectives in carbon dioxide usage for the sustainable production of energy and chemicals and to reduce global warming. We discuss the heterogeneously catalysed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates. Various sources of hydrogen are also reviewed in terms of their CO2 neutrality. Technologies have been developed for large-scale CO2 hydrogenation to methanol or methane. Their industrial application is, however, limited by the high price of renewable hydrogen and the availability of large-volume sources of pure CO2. With regard to the direct electrocatalytic reduction of CO2 to value-added chemicals, substantial advances in electrodes, electrolyte, and reactor design are still required to permit the development of commercial processes. Therefore, in this review particular attention is paid to (i) the design of metal electrodes to improve their performance and (ii) recent developments of alternative approaches such as the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. The most significant improvements both in catalyst and reactor design are needed for the photocatalytic functionalisation of CO2 to become a viable technology that can help in the usage of CO2 as a feedstock for the production of energy and chemicals. Apart from technological aspects and catalytic performance, we also discuss fundamental strategies for the rational design of materials for effective transformations of CO2 to value-added chemicals with the help of H2, electricity and/or light.

Oxidative Coupling of Methane

The sections in this article are Introduction Fundamentals of the OCM Reaction Catalytic Materials and Their Performance Mechanistic Aspects Oxygen Species in the OCM Reaction Structural Defects and Related Physicochemical Properties New Approaches in Catalyst Design Reaction and Process Engineering Chemical Kinetics Modeling, Simulation and Performance of Catalytic Reactors Distributed Oxygen Supply to a Catalytic Fixed-Bed Reactor Counter-Current Moving-Bed Reactor Fluidized-Bed Reactors Membrane Reactors Process Concepts Conclusion Keywords: methane; oxidative coupling; natural gas; ethane; ethene; OCM catalysts; kinetics; mechanism; reactor design; product separation

Towards the "pressure and materials gap": Hydrogenation of acrolein using silver catalysts

Abstract The hydrogenation of acrolein has been studied over various Ag/SiO2 catalysts in a pressure range from 50mbar to 20bar. Increasing partial pressures of acrolein and/or hydrogen lead to increasing selectivities of allyl alcohol. The selectivity towards allyl alcohol also depends on the structural features of the Ag/SiO2 catalyst. Larger particles seem to favour the production of propanal. This observation is discussed in view of the different plane-to-edge-ratio of the different catalysts. The interaction of hydrogen with silver samples has been studied with TAP at very low pressures as well as with calorimetry at ambient pressures. Both methods indicate, that also the hydrogen adsorption is structure-sensitive. No interaction of hydrogen with electrolytic silver or the support material alone was observed. IR spectroscopy has been used to elucidate the interaction of acrolein with Ag/SiO2 catalysts. A strong interaction with the support material was found, hindering the observation of probable silver-acrolein interaction.

ZrO2-Based Alternatives to Conventional Propane Dehydrogenation Catalysts: Active Sites, Design, and Performance

Non-oxidative dehydrogenation of propane to propene is an established large-scale process that, however, faces challenges, particularly in catalyst development; these are the toxicity of chromium compounds, high cost of platinum, and catalyst durability. Herein, we describe the design of unconventional catalysts based on bulk materials with a certain defect structure, for example, ZrO2 promoted with other metal oxides. Comprehensive characterization supports the hypothesis that coordinatively unsaturated Zr cations are the active sites for propane dehydrogenation. Their concentration can be adjusted by varying the kind of ZrO2 promoter and/or supporting tiny amounts of hydrogenation-active metal. Accordingly designed Cu(0.05 wt %)/ZrO2 -La2 O3 showed industrially relevant activity and durability over ca. 240 h on stream in a series of 60 dehydrogenation and oxidative regeneration cycles between 550 and 625 °C.

Effect of support on selectivity and on-stream stability of surface VOx species in non-oxidative propane dehydrogenation

Al2O3, SiO2(MCM-41), and Al2O3–SiO2 (Siral®) with a SiO2 content varying from 1 to 70 wt.% were used to prepare supported catalysts with a V loading below one monolayer. Their activity, selectivity and on-stream stability were tested in non-oxidative propane dehydrogenation (DH) at 550 °C. The highest space–time yield of propene was only 25% lower than that over industrially relevant Pt–Sn/Al2O3 under the same reaction conditions. All catalysts deactivated with time on stream, but restored their initial performance after oxidative regeneration as proven in a sequence of 10 DH/regeneration cycles lasting in total over 60 h. The deactivation was related to propene-derived carbon deposits covering active VOx sites. However, depending on the catalyst, such deposits formed on bare support sites can also participate in propane dehydrogenation. Their DH activity is, however, significantly lower compared to VOx species. Acidic properties of the support were found to be crucial for the generation of such catalytically active carbon species.

Tailored Noble Metal Nanoparticles on γ‐Al2O3 for High Temperature CH4 Conversion to Syngas

The simple deposition of tailored Rh or Pt nanoparticles (NP) on γ‐Al2O3 results in active, selective, and stable catalysts for partial oxidation of methane (POM) to syngas. The NP were prepared by the ethylene glycol method in strong alkaline solution. This approach was found to be a promising way of providing active metallic NP for catalyzing the POM reaction. NP sizes determined by small angle X‐ray scattering (SAXS) in solution and by transmission electron microscopy (TEM) on alumina were very close. This result highlights the possibility of easy pre‐characterization of NP by the former method. Supported Rh NP are intrinsically more active in the POM reaction than Pt NP and also showed a superior performance compared with a conventionally prepared Rh catalyst, even if the latter had been pre‐reduced. Mechanistic investigations in the temporal analysis of products (TAP) reactor indicate that the higher selectivity of well‐defined Rh‐NP is determined by their lower activity for consecutive CO transformations.

Catalytic Abatement of Nitrous Oxide Coupled with Selective Production of Hydrogen and Ethylene

In the past two decades, global warming caused by anthropogenic emissions of greenhouse gases has become an intensively discussed topic of public and scientific interest. The Kyoto protocol to the United Nations Framework Convention on Climate Change is a practical step to control the emissions of environmentally harmful gases. The protocol obliges participating countries to reduce emission of CO2 as well as non-CO2 greenhouse gases. One of the non-CO2 greenhouse gases is nitrous oxide (N2O), which has a 310 times greater potential than CO2 to warm up the atmosphere. Moreover, N2O contributes to the destruction of ozone in the stratosphere. One of the anthropogenic sources of N2O is the production of adipic and nitric acids, both of which are key components in the manufacture of a variety of commercial products. The estimated annual production (without abatement) of N2O in these processes [1,2] is approximately 1.3 Mton, which corresponds to about 20% of the overall anthropogenic N2O emissions. [3] There are several commercial N2O removal technologies [3–6] that are based on catalytic or thermal conversion of N2O to N2 and O2. When N2O is abated by selective catalytic reduction, the reducing agents, such as natural gas and/or ammonia, are converted into COx and N2, respectively. However, a process that combines N2O removal with the simultaneous production of important chemical products would be both more sustainable and economically attractive. In this regard Solutia Inc., in collaboration with the Boreskov Institute of Catalysis (BIC), developed a technology that employs pure N2O as an oxidant to produce phenol from benzene over Fe-MFI zeolites. Fe-MFI zeolites are also promising catalysts for the oxidative dehydrogenation of propane to propene using N2O as an oxidant. [9,10] These elegant approaches, however, suffer from fast catalyst deactivation and low selectivity when N2O is contaminated with O2 and NOx, which is the case with off-gases from the production of adipic and nitric acids. Unfortunately, the purification of off-gases results in a substantial cost increase of the above processes, which makes them uneconomical. Thus, better catalysts tolerant to O2 and NOx are key to allow for the development of green processes using waste N2O. Herein, we present a novel process and catalyst for N2O decomposition to N2 with simultaneous production of H2 and C2H4 from C2H6. Our concept is based on the use of the exothermic N2O decomposition for the thermal dehydrogenation of ethane. Calcium oxide doped with small amounts of sodium oxide (Na/CaO) was used as a catalyst. To determine whether the procedure for catalyst preparation is reproducible, two catalyst charges were prepared with sodium concentrations of 0.9 and 1.5 at.% (Na0.009CaO and Na0.015CaO). It was found that the catalysts are active for direct N2O decomposition. For example, a nearly complete (ca. 99%) N2O conversion was achieved when an N2O–Ne mixture (40 vol.% N2O in Ne) was fed over Na0.009CaO at 903 K with a contact time of 0.048 sgcatmL . As a result of the exothermicity of N2O decomposition, the catalyst temperature rose above 1100 K. The N2O conversion without catalyst did not exceed 5% at 903 K and no temperature increase was detected. However, the catalyst temperature increased above 1100 K when a mixture of N2O and C2H6 (N2O/C2H6/Ne= 40:40:20) was fed over Na/CaO at 903 K with a contact time of 0.048 sgcatmL . Moreover, N2O is almost completely (X(N2O)> 99%) converted into N2, while C2H6 is converted (X(C2H6)> 50%) into C2H4 and H2; CH4, COx, and H2O were also observed as reaction products. The conversion of N2O and C2H6 did not exceed 10 and 18%, respectively, when the same N2O–C2H6 mixture was fed to the reactor without catalyst (filled with 250–350-mm SiO2 particles) at 1023 K. Thus, Na0.009CaO and Na0.015CaO catalyze direct N2O decomposition and N2O abatement with C2H6. The catalytic performance of Na/CaO materials in N2O removal with simultaneous generation of C2H4 and H2 from C2H6 is shown in Table 1. The N2O conversion (X) to N2 was above 99%. No significant difference in the catalytic performance of Na0.009CaO and Na0.015CaO was observed, which indicates the good reproducibility of the method of catalyst preparation. Ethane is converted into ethylene with approximately 50% yield (Y) and 63% selectivity (S). Other C-

Methane conversion into different hydrocarbons or oxygenates: current status and future perspectives in catalyst development and reactor operation

This Perspective highlights recent developments in methane conversion into different hydrocarbons and oxygenates (methanol, its derivatives, and formaldehyde) with the purpose to address the global demand for efficient and environmentally friendly production of these bulk chemicals. Our analysis identified possible directions for further research to bring the above approaches to a commercial level. As no progress in the development of catalysts for the oxidative coupling of methane could be identified, improvements are expected through reactor operation, cost- and energy-efficient methods for product separation and for providing pure oxygen. With respect to methane oxidation to methanol, further progress can also be achieved by proper catalyst design on the basis of fundamental knowledge especially gained from homogeneous and enzymatic catalysts as well as from theoretical calculations.

The Enhancing Effect of Brønsted Acidity of Supported MoOx Species on their Activity and Selectivity in Ethylene/trans-2-Butene Metathesis

Supported catalysts with a nominal Mo surface density of 0.15 and 1.5 Mo atoms nm−2 were synthesized by impregnation of alumina, silica, and alumina–silica supports with silica content between 1 and 70 wt %. They were tested for their activity and selectivity in the metathesis of ethylene and trans‐2‐butene to propene between 343 and 603 K at 125 kPa. The catalysts were characterized by UV/Vis, Raman, and IR spectroscopy, XRD and H2 temperature‐programmed reduction for elucidating the distribution, degree of polymerization, reducibility, and acidity of MoOx species. We established that Brønsted acidity of highly dispersed tetrahedral and polymerized octahedral MoOx species is required to ensure high metathesis activity. The acidic character of these species is influenced by their structure and support. Tetrahedral MoOx species with Brønsted acidic character are only formed on supports possessing such acidity, whereas Brønsted acidic octahedral MoOx is also created on supports without such acidic sites.

Effect of VOx Species and Support on Coke Formation and Catalyst Stability in Nonoxidative Propane Dehydrogenation

VOx/SiO2–Al2O3 catalysts were prepared by grafting vanadyl acetylacetonate onto the supports with a SiO2 content between 0 and 100 wt. %. The degree of polymerization of VOx species and acidity both of pristine supports and the catalysts were evaluated. To determine their on‐stream stability and carbon deposition activity in nonoxidative propane dehydrogenation, continuous‐flow tests and in situ thermogravimetric measurements were performed. The rate constants of catalyst deactivation and carbon deposition were derived from kinetic evaluation of these experiments. Gathered experimental evidence pointed out that VOx species were significantly more active for coke formation than acid sites of the supports. The rate constant of carbon formation was found to increase with the degree of polymerization of VOx species, whereas no correlation between catalyst acidity and the rate constants of coking or deactivation could be drawn.