Catalytic carbon dioxide (CO ₂ ) hydrogenation is a potential route for producing sustainable fuels and chemicals, but existing catalysts need improvement. In particular, identifying active sites and understanding the interaction between components and the dynamic behavior of the participant species remain unclear. This fundamental knowledge is essential for the design of more efficient and stable catalysts. Because the nature of the active site (metal, oxide, carbide) is the main factor that determines the catalytic activity of the catalysts, this Review focuses on various types of heterogeneous catalysts that have been recently reported in the literature as efficient for CO ₂ conversion to C1 [carbon monoxide (CO), methanol (CH ₃ OH), methane (CH ₄ )], and higher hydrocarbons. We focus on establishing key connections between active-site structures and selectivity, regardless of catalyst composition.

Emerging technologies are expected to contribute to environmental sustainable development. However, throughout the development of novel technologies, it is unknown whether emerging technologies can lead to reduced environmental impacts compared to a potentially displaced mature technology. Additionally, process steps suspected to be environmental hotspots can be improved by process engineers early in the development of the emerging technology. In order to determine the environmental impacts of emerging technologies at an early stage of development, prospective life cycle assessment (LCA) should be performed. However, consistency in prospective LCA methodology is lacking. Therefore, this article develops a framework for a prospective LCA in order to overcome the methodological inconsistencies regarding prospective LCAs. The methodological framework was developed using literature on prospective LCAs of emerging technologies, and therefore, a literature review on prospective LCAs was conducted. We found 44 case studies, four review papers, and 17 papers on methodological guidance. Three main challenges for conducting prospective LCAs are identified: Comparability, data, and uncertainty challenges. The issues in defining the aim, functionality, and system boundaries of the prospective LCAs, as well as problems with specifying LCIA methodologies, comprise the comparability challenge. Data availability, quality, and scaling are issues within the data challenge. Finally, uncertainty exists as an overarching challenge when applying a prospective LCA. These three challenges are especially crucial for the prospective assessment of emerging technologies. However, this review also shows that within the methodological papers and case studies, several approaches exist to tackle these challenges. These approaches were systematically summarized within a framework to give guidance on how to overcome the issues when conducting prospective LCAs of emerging technologies. Accordingly, this framework is useful for LCA practitioners who are analyzing early-stage technologies. Nevertheless, further research is needed to develop appropriate scale-up schemes and to include uncertainty analyses for a more in-depth interpretation of results.

Life cycle interpretation is the fourth and last phase of life cycle assessment (LCA). Being a “pivot” phase linking all other phases and the conclusions and recommendations from an LCA study, it represents a challenging task for practitioners, who miss harmonized guidelines that are sufficiently complete, detailed, and practical to conduct its different steps effectively. Here, we aim to bridge this gap. We review available literature describing the life cycle interpretation phase, including standards, LCA books, technical reports, and relevant scientific literature. On this basis, we evaluate and clarify the definition and purposes of the interpretation phase and propose an array of methods supporting its conduct in LCA practice. The five steps of interpretation defined in ISO 14040–44 are proposed to be reorganized around a framework that offers a more pragmatic approach to interpretation. It orders the steps as follows: (i) completeness check, (ii) consistency check, (iii) sensitivity check, (iv) identification of significant issues, and (v) conclusions, limitations, and recommendations. We provide toolboxes, consisting of methods and procedures supporting the analyses, computations, points to evaluate or check, and reflective processes for each of these steps. All methods are succinctly discussed with relevant referencing for further details of their applications. This proposed framework, substantiated with the large variety of methods, is envisioned to help LCA practitioners increase the relevance of their interpretation and the soundness of their conclusions and recommendations. It is a first step toward a more comprehensive and harmonized LCA practice to improve the reliability and credibility of LCA studies.

Carbon capture and utilization is a promising approach to reduce greenhouse gas emissions and fossil resource depletion in the chemical industry. However, since carbon capture and utilization is an energy and material intensive process, it is unclear whether it allows for a net reduction of environmental impacts from a life cycle perspective. Previous life cycle assessment studies on carbon capture and utilization focused on the production of one specific chemical or the comparison of C₁ basic chemicals and applied an attributional approach. This study assesses twelve CO₂-conversion technologies to provide decision support on the potential life-cycle environmental impacts of each technology. Consequential life cycle assessment was chosen as the modeling approach to better understand the system-wide environmental consequences of introducing carbon capture and utilization technologies in the chemical industry. This study has identified that in a near- and a long-term scenario the global warming impact for all CO₂ conversions technologies, besides dimethoxymethane, electrochemically produced formic acid, and Fischer–Tropsch production, is negative. Formic acid produced via hydrogenation and polyol production are the conversion technologies with the highest potential for reducing the global warming impact from a life cycle perspective. Holistically polyol production is the conversion technology with the highest potential for reducing environmental impacts. In general, it seems recommendable to introduce carbon capture and utilization within the chemical industry from an environmental perspective.