Producing energy from CO₂ rather than absorbing and disposing of it is a sustainable energy technique. In reality, several thermochemical processes may transform CO₂ into value-added compounds such as hydrogen, methanol, and ethanol [31]. These fuels may be utilized to power automobiles without requiring major modifications to existing internal combustion engines, paving the way for a more sustainable future. Discovering eco-friendly alternatives and new energy scenarios, primarily the conversion of CO₂ into value-added chemicals using sunlight, is one of the top-most research priorities to overcome today’s extreme reducing the use of fossil fuels and mitigate the global warming risks associated with high CO₂ concentrations in the atmosphere [32].

Because of decreased prices, quick commercial adoption, and complete industrial development, the use of second-generation green fuels is one of the most promising approaches to achieving industrial and ecological aims in the short term. A green fuel, unlike fossil fuel, does not emit more CO₂ into the atmosphere since its burning, in the well-to-wheel cycle, creates a CO₂ release equivalent to that required for its manufacture, closing the CO₂ balance, and making it a carbon-neutral fuel [33]. The practical application of hydrogenation catalysts in conjunction with commercially viable research and innovation technology. Indeed, catalytic conversion of atmospheric CO₂ into biofuels and fine chemicals would be one of the most economical and realistic solutions to the problem of greenhouse gas emissions, assuming that capture/sequestration and high-pressure storage technologies become commercially viable [34,35]. Nonetheless, in a very short time, the most prosecutable actions and encouraging prospects look upon the use of CO₂-rich streams originating from industrial exhaust emissions, such as brick and cement work, despite the need for clean-up stages, as well as additional purification and concentration [36]. Haldor-Topsoe is at the vanguard of using CO₂ as a carbon feedstock through various power-to-gas technologies, whereas ENI is redesigning its production lines with a greener vision, by developing new hydrogenation processes, called ENI Ecofining^TM, for green-fuels synthesis, advantageously depicting the production of ultra-pure CO₂ as industrial practice [37]. Despite significant advances in fuel science, the commercial and economic viability of hydrogen-to-liquid-fuels such as methanol is still being debated. The discovery of more effective catalyst substances for the efficient hydrogenation of CO₂ looks to be of major importance in this scenario. CuO/ZnO-based catalysts, as is well known, offer lower costs and improved chemical stability when compared to other catalysts such as transition metal carbides (TMCs), bimetallic catalysts, or Au-supported catalysts [38]. Although CuO/ZnO/Al₂O₃ is the most extensively investigated catalyst for methanol synthesis, it was shown that the inclusion of ZrO₂, CeO₂, and TiO₂ oxides improved both the activity and selectivity of CuO/ZnO-based catalysts in CO₂ hydrogenation processes [39].

Recently the influence of replacing Al₂O₃ with CeO₂ in the typical Cu-ZnO/Al₂O₃ catalytic discussed composition for syngas conversion, suggesting that the use of cerium oxide led to a remarkable positive effect on the catalyst stability, as a result of the preservation of the ratio of CuO/Cu⁺ on the catalyst surface. As well as, on the particle growth, due to the strong electron interactions of the copper/ceria phase (Cu/Cu₂O/CuO, Ce³⁺/Ce⁴⁺) during hydrogenation reactions [40]. Metal dispersion and CO₂ adsorption capacity are two key parameters affecting the CO₂ hydrogenation functionality of Cu-based systems. Similarly, in our previous works, we displayed that the use of several oxides (i.e., ZnO, ZrO₂, CeO₂, Al₂O₃, Gd₂O₃, Ce₂O₃, and Y₂O₃) and alkaline metals (i.e., Li, Cs, and K) could remarkably influence both catalyst structure and morphology, balancing the amount of the diverse copper species (i.e., Cu°/Cu⁺/Cu²⁺) and leading to a notable improvement of the catalytic performance. On this account, ZrO₂ has been shown to positively the affect morphology and texture of Cu-ZnO based catalysts, also favoring CO₂ adsorption / activation and methanol selectivity, while CeO₂ could act as both an electronic promoter and improver of surface functionality of Cu phase [41]. As reported in our preliminary works, the scientists have proved a greater specific activity of CuZnO-CeO₂ catalyst with respect to that of similar catalytic systems containing ZrO₂ or other promoter oxides, facing several electronic and structural effects. Despite of a generally higher specific activity, we have evidenced that the CuZnO-Ceria catalyst suffers from several practical limitations, such as: a lower surface area, especially compared to that of ZrO₂ and Al₂O₃ promoted catalysts.

Hydrogen has several benefits as an energy carrier and will play a key role in future energy production and circular economy [42]. Because hydrogen can be created in a climate-neutral way and emits only water when used, it is regarded as a climate-friendly energy carrier [43]. Hydrogen derived from renewable sources is commonly referred to as “green hydrogen.” It contrasts with “grey hydrogen,” which is defined as hydrogen derived from fossil, nonrenewable sources [44]. Currently, grey hydrogen generated by steam reforming of fossil natural gas accounts for the majority of worldwide hydrogen production [44]. Grey hydrogen may be converted to “blue hydrogen” by using carbon capture and storage technology, but it remains a non-renewable source [45]. To distinguish between carbon-neutral green and blue hydrogen, we coined the term “carbon-negative hydrogen.” Hydrogen has a wide range of uses due to its high gravimetric energy density, as well as its ease of storage and transportation [46]. Fuel cells may produce both electric power and heat from hydrogen. In the steel industry, hydrogen may also be utilized as a reducing agent [46]. It is regarded as an unavoidable basic building element in difficult-to-electrify zones [46]. Green hydrogen may be created using renewable power or renewable biomass, either through thermochemical processes or using microorganisms and biotechnological technologies. Biohydrogen, or hydrogen generated from biomass, can lead to more effective use of biogenic source materials by using residual and waste materials. Biohydrogen production technologies are classified as thermochemical or biotechnological. Biohydrogen may be generated on an industrial scale utilizing thermochemical methods from biomass (wood, straw, grass clippings, etc.) as well as other bioenergy sources (biogas, bioethanol, etc.) [43]. Gasification and pyrolysis are two types of thermochemical reactions. The synthesis gas produced by gasification or pyrolysis contains varying proportions of H₂, CO₂, carbon monoxide (CO), methane (CH₄), and other components such as nitrogen, water vapor, light hydrocarbons, hydrochloric acid, alkali chlorides, Sulphur compounds, biochar, or tar [47]. The following chemical processes occur as a result of subsequent steam reforming and/or water gas shift reactions, culminating in the creation of CO₂ and hydrogen [48]. Minimal carbon-hydrogen (MCH) should be used initially in areas that are difficult to electrify directly [49]. We believe that generated bio-hydrogen is employed in difficult-to-electrify industrial sectors such as cement, steel, refining, ammonia, and glass. Refineries and ammonia plants are now the largest customers of hydrogen generated by steam methane reforming, a process that releases at least 10 kg CO₂ for every kilogram H₂ produced. Because many industries utilize carbon-intensive hydrogen, switching to MCH would be a near-term opportunity to increase hydrogen demand while lowering greenhouse gas emissions. Companies that are difficult to electrify may reduce their emissions and capture carbon dioxide by switching to alternative fuels and implementing carbon capture and storage technologies. This can help to enable their operations to contribute to the elimination of carbon dioxide from the atmosphere.

Country-specific forecasts of European nations’ ultimate energy consumption in 2050 are unavailable and difficult to determine. As a result, scientists evaluate country-specific final energy consumption in 2019 and anticipate that 5–30% of final energy consumption will be fulfilled with low-carbon hydrogen to minimize hard-to-electrify emissions. These scenarios enable us to set upper and lower bounds on the amount of hydrogen likely required by each European country to achieve net-zero emissions by 2050 [50].