A review on high-pressure heterogeneous catalytic processes for gas-phase CO2 valorization

This review discusses the importance of mitigating CO2 emissions by valorizing CO2 through high-pressure catalytic processes. It focuses on various key processes, including CO2 methanation, reverse water-gas shift, methane dry reforming, methanol, and dimethyl ether synthesis, emphasizing pros and cons of high-pressure operation. CO2 methanation, methanol synthesis, and dimethyl ether synthesis reactions are thermodynamically favored under high-pressure conditions. However, in the case of methane dry reforming and reverse water-gas shift, applying high pressure, results in decreased selectivity toward desired products and an increase in coke production, which can be detrimental to both the catalyst and the reaction system. Nevertheless, high-pressure utilization proves industrially advantageous for cost reduction when these processes are integrated with Fischer-Tropsch or methanol synthesis units. This review also compiles recent advances in heterogeneous catalysts design for high-pressure applications. By examining the impact of pressure on CO2 valorization and the state of the art, this work contributes to improving scientific understanding and optimizing these processes for sustainable CO2 management, as well as addressing challenges in high-pressure CO2 valorization that are crucial for industrial scaling-up. This includes the development of cost-effective and robust reactor materials and the development of low-cost catalysts that yield improved selectivity and long-term stability under realistic working environments.

Is the RWGS a viable route for CO2 conversion to added value products? A techno-economic study to understand the optimal RWGS conditions

Understanding the viability of the RWGS from a thermodynamic and techno-economic angle opens new horizons within CO₂ conversion technologies. Unfortunately, profitability studies of this technology are scarce in literature and mainly focused on overall conversion and selectivity trends with tangential remarks on energy demands and process costs. To address this research gap, herein we present a comprehensive techno-economic study of the RWGS reaction when coupling with Fischer-Tropsch synthesis is envisaged to produced fuels and chemicals using CO₂ as building block. We showcase a remarkable impact of operating conditions in the final syngas product and both CAPEX and OPEX. From a capital investment perspective, optimal situations involve RWGS unit running at low temperatures and high pressures as evidenced by our results. However, from the running cost angle, operating at 4 bar is the most favorable alternative within the studied scenarios. Our findings showcase that, no matter the selected temperature the RWGS unit should be preferentially run at intermediate pressures. Ultimately, our work maps out multiple operating scenarios in terms of energy demand and process cost serving as guideline to set optimal reaction conditions to unlock the potential of the RWGS for chemical CO₂ recycling.

K-Promoted Ni-Based Catalysts for Gas-Phase CO2 Conversion: Catalysts Design and Process Modelling Validation

The exponential growth of greenhouse gas emissions and their associated climate change problems have motivated the development of strategies to reduce CO₂ levels via CO₂ capture and conversion. Reverse water gas shift (RWGS) reaction has been targeted as a promising pathway to convert CO₂ into syngas which is the primary reactive in several reactions to obtain high-value chemicals. Among the different catalysts reported for RWGS, the nickel-based catalyst has been proposed as an alternative to the expensive noble metal catalyst. However, Ni-based catalysts tend to be less active in RWGS reaction conditions due to preference to CO₂ methanation reaction and to the sintering and coke formation. Due to this, the aim of this work is to study the effect of the potassium (K) in Ni/CeO₂ catalyst seeking the optimal catalyst for low-temperature RWGS reaction. We synthesised Ni-based catalyst with different amounts of K:Ni ratio (0.5:10, 1:10, and 2:10) and fully characterised using different physicochemical techniques where was observed the modification on the surface characteristics as a function of the amount of K. Furthermore, it was observed an improvement in the CO selectivity at a lower temperature as a result of the K-Ni-support interactions but also a decrease on the CO₂ conversion. The 1K catalyst presented the best compromise between CO₂ conversion, suppression of CO₂ methanation and enhancing CO selectivity. Finally, the experimental results were contrasted with the trends obtained from the thermodynamics process modelling observing that the result follows in good agreement with the modelling trends giving evidence of the promising behaviour of the designed catalysts in CO₂ high-scale units.

Carbothermally generated copper–molybdenum carbide supported on graphite for the CO2 hydrogenation to methanol

The carbothermal synthesis of monometallic and bimetallic molybdenum carbide and copper supported on high surface area graphite, has been studied at 600 and 700 °C and characterised. The catalysts were tested for CO₂ hydrogenation to CH₃OH.