A brief review on the reaction mechanisms of CO2 hydrogenation into methanol

Abstract

The catalytic reduction of CO2 to methanol is an appealing option to reduce greenhouse gas concentration as well as renewable energy production. In addition, the exhaustion of fossil fuel, increase in earth temperature and sharp increases in fuel prices are the main driving factor for exploring the synthesis of methanol by hydrogenating CO2. Many studies on the catalytic hydrogenation of CO2 to methanol were published in the literature over the last few decades. Many of the studies have presented different catalysts having high stability, higher performance, low cost, and are immediately required to promote conversion. Understanding the mechanisms involved in the conversion of CO2 is essential as the first step towards creating these catalysts. This review briefly summarizes recent theoretical developments in mechanistic studies focused on using density functional theory, kinetic Monte Carlo simulations, and microkinetics modeling. Based on these simulation techniques on different transition metals, metal/metal oxide, and other heterogeneous catalysts surfaces, mainly, three important mechanisms that have been recommended are the formate (HCOO), reverse water–gas shift (RWGS), and trans-COOH mechanisms. Recent experimental and theoretical efforts appear to demonstrate that the formate route in which the main intermediate species is H2CO* in the reaction route, is more favorable in catalytic hydrogenation of CO2 to chemical fuels in various temperature and pressure conditions.

An insight of CO 2 hydrogenation to methanol synthesis: Thermodynamics, catalysts, operating parameters, and reaction mechanism

“…6 Qaderi et al have studied the mechanism of the CO 2 hydrogenation reaction, the suggested reaction mechanisms are the "Formate" intermediate formation mechanism, "Reverse water-gas shift" mechanism, and "Trans-COOH" mechanism. 121 A summary of each of the three probable mechanisms is explained in the subsequent sections.…”

Addressing the CO2 challenge through thermocatalytic hydrogenation to carbon monoxide, methanol and methane

“…164 Nevertheless, this conclusion cannot be applied to all the materials used for this reaction, and the pathway going through the RWGS reaction was also reported. 165 While the reaction pathway strongly depends on the catalytic system, the reaction parameters can also play a crucial role. As an example, the reactivity of (111) facets of palladium and palladium–zinc alloy have highlighted a RWGS pathway and a formate pathway, respectively.…”

From CO2 to Methanol on Cu/ZnO/Al2O3 Industrial Catalyst. What Do We Know about the Active Phase and the Reaction Mechanism?

“…Methanol synthesis from syngas or CO 2 using the classic industrial catalyst based on a mixture of metallic copper, ZnO nanoparticles, and alumina (Al 2 O 3 ) as a promoter is a topic that has been discussed and reviewed in several papers in the last two decades. − The question then is why another review article? One reason is that the literature on this subject is simply enormous, not surprisingly given that the reaction has been known and used industrially for more than 50 years, and it is not easy to find in a concise and structured report what can be extracted from all these efforts as general and universally accepted messages.…”

“…None of these questions are new, and answers can be found from many excellent and rigorous studies in the existing literature or from extensive reviews. − It is much more difficult to find a concise, synthetic but exhaustive summary, yet based on clear evidence. If you ask the question to ChatGPT, you will receive this answer: “The active phase in the Cu/ZnO/Al 2 O 3 industrial catalyst for methanol synthesis typically refers to the copper (Cu) component of the catalyst (...).…”