The Oxygenate-Mediated Conversion of CO_x to Hydrocarbons─On the Role of Zeolites in Tandem Catalysis

Abstract

Decentralized chemical plants close to circular carbon sources will play an important role in shaping the postfossil society. This scenario calls for carbon technologies which valorize CO 2 and CO with renewable H 2 and utilize process intensification approaches. The single-reactor tandem reaction approach to convert CO x to hydrocarbons via oxygenate intermediates offers clear benefits in terms of improved thermodynamics and energy efficiency. Simultaneously, challenges and complexity in terms of catalyst material and mechanism, reactor, and process gaps have to be addressed. While the separate processes, namely methanol synthesis and methanol to hydrocarbons, are commercialized and extensively discussed, this review focuses on the zeolite/zeotype function in the oxygenate-mediated conversion of CO x to hydrocarbons. Use of shape-selective zeolite/ zeotype catalysts enables the selective production of fuel components as well as key intermediates for the chemical industry, such as BTX, gasoline, light olefins, and C 3+ alkanes. In contrast to the separate processes which use methanol as a platform, this review examines the potential of methanol, dimethyl ether, and ketene as possible oxygenate intermediates in separate chapters. We explore the connection between literature on the individual reactions for converting oxygenates and the tandem reaction, so as to identify transferable knowledge from the individual processes which could drive progress in the intensification of the tandem process. This encompasses a multiscale approach, from molecule (mechanism, oxygenate molecule), to catalyst, to reactor configuration, and finally to process level. Finally, we present our perspectives on related emerging technologies, outstanding challenges, and potential directions for future research. CONTENTS 1. Introduction 11775 2. Methanol-Mediated CO x Conversion to Hydrocarbons 11783 2.1. A Short Introduction to the MTH Process 11783 2.2. Integration of the MTH Reactions with CO x Hydrogenation 11787 3. Dimethyl-Ether-Mediated CO x Conversion to Hydrocarbons 11791 3.1. Dimethyl Ether to Hydrocarbons (DTH) 11791 3.2. Methanol to Dimethyl Ether (MTD) 11793 3.3. Integration of the MTD and DTH Reactions with CO x Hydrogenation 11794 4. Ketene-Mediated CO x Conversion to Hydrocarbons 11798 4.1. Methanol Carbonylation 11798 4.2. DME Carbonylation 11799 4.3. Integration of Methanol and DME Carbonylation with CO x Hydrogenation 11803 5.

Transitioning from Methanol to Olefins (MTO) toward a Tandem CO2 Hydrogenation Process: On the Role and Fate of Heteroatoms (Mg, Si) in MAPO-18 Zeotypes

“…A higher involvement of formaldehyde-mediated reactions may also be the reason for the promotion of the Prins reaction, the bigger role of the aromatic cycle (see the lower C 4 /C 2 ratio of SAPO-18 at a low temperature in Figure 2 g), and therefore the faster deactivation ( Figure 1 a,b), all in agreement with the previous results from the Lercher group. 41 Otherwise, the lack of CO 2 over MgAPO-18 suggests that the CO-mediated carbonylation/decarbonylation reaction cycles 3 should be the main source of the first olefins and that decarboxylation pathways are less favored in this case. This, together with our previously observed faster methylation rates on Mg-substituted AlPO materials, 23 may explain the longer lifetime of MgAPO-18.…”

“…The tandem catalyst generally consists of a metal and/or metal oxide component to form the oxygenate and a zeolite/zeotype component to convert the oxygenate to hydrocarbons. This commonly named OXZEO catalyst achieves product distributions beyond the Fischer–Tropsch limitation, yet in a broader range to what is obtained in the conversion of methanol to hydrocarbons (MTH) over the same zeolite/zeotype . Some differences exist, which have been ascribed partly to the presence of additional components in the gas feed, in particular, high-pressure H 2 , CO, and H 2 O. − …”

“… 3 Some differences exist, which have been ascribed partly to the presence of additional components in the gas feed, in particular, high-pressure H 2 , CO, and H 2 O. 3 − 7 …”

Hydrogen Activation with Ru-PN3P Pincer Complexes for the Conversion of C1 Feedstocks

“…The efficient production of green hydrogen and its conversion to renewable liquid energy carriers such as formic acid or methanol, so-called power-to-liquids (P2L) processes, are gaining increased interest due to the urgent need for sustainable fuels. − Green hydrogen refers to H 2 obtained from a renewable source, for example, through water electrolysis using renewable electricity or from the gasification of biomass. Hydrogenations of C 1 feedstocks such as CO or CO 2 are important in this context as this can give access to a range of green chemicals, including HCO 2 H, MeOH, and hydrocarbons. − The hydrogenation of CO is currently applied in several large-scale chemical processes such as the Fischer–Tropsch process and the production of MeOH (110 Mt per annum), all based on heterogeneous catalysis.…”

Spinel Nanostructures for the Hydrogenation of CO2 to Methanol and Hydrocarbon Chemicals

“…The first is the modified Fischer–Tropsch (FT) catalyst that couples a reverse water gas shift (RWGS, CO 2 + H 2 = CO + H 2 O) and an FT synthesis reaction. − However, the C–C growth over the FT catalyst follows the polymerization mechanism, producing only linear hydrocarbon products with a wide distribution . The second approach is the tandem catalyst composed of metal oxide and zeolites (zeotypes), which couples methanol synthesis and methanol-to-hydrocarbon (MTH) reactions. − Different from modified FT synthesis, the tandem catalysis separates CO 2 activation and C–C coupling on the two active sites, and the product selectivity is decided by the topology and acidity of zeolites/zeotypes, thus providing an alternative strategy for the selective hydrogenation of CO 2 into multicarbon compounds. It is noteworthy that in the tandem catalysts, the component for methanol synthesis is not the typical low-temperature (200–250 °C) Cu-based catalyst but the high-temperature (280–400 °C) and reducible oxide-based catalysts, such as InO x , CrO x , InZrO x , ZnZrO x , and ZnGaO x , to match the subsequent MTH reaction, working at temperatures above 300 °C. − …”