Ana Reis Machado ^1* Ana V.M. NUNES ^2* Manuel Nunes da Ponte ³

• ¹ CENIMAT I3N and LAQV REQUIMTE, Nova School of Science and Technology, Faculty of Science and Technology, New University of Lisboa, Caparica, Portugal
• ² LAQV REQUIMTE, Nova School of Science and Technology, Faculty of Science and Technology, New University of Lisboa, Caparica, Portugal
• ³ LAQV -REQUIMTE, Nova School of Science and Technology, Faculty of Science and Technology, New University of Lisboa, Caparica, Portugal

that can be adopted by industry to reach Near Zero Emissions Scenario (NZE) in three important sectors, namely in the production of surfactants, in the production of fuels on the hard to electrify heavy goods transportation and in construction materials based on biomass wastes and CO 2 mineralization. Emerging research trends that will define the role of CO 2 on the future of the global economy are described.In the first article, Newman et al. (2023) highlight the importance to harmonize CCU sustainability assessments in order to guide R&D investments towards sustainable processes, products and supply chains. In addition to environmental and economic analyses, societal issues were recently included in the assessments, forming the triple helix framework McCord et al. (2021). In this paper, the different methodologies were reviewed. While combined Life Cycle and Techno-Economic Assessments have reached maturity, societal sustainability assessment still presents significant challenges, due to qualitative data and scarcity of quantitative inputs and analysis methodology. Future work should achieve methodological harmonization in sustainability evaluation of CCU projects integrating societal sustainability assessment.The need to screen several chemical pathways before a process is adopted to assure sustainable production is becoming more evident. Several attempts have been made using different analysis frameworks. In the second paper, Platt et al. (2022) showed the wide potential for green Linear Alkylbenzene Sulfonate (LAS) production. They used different building blocks by constructing a tree diagram based on literature search and technology evaluation, highlighting the need for a short form sustainability screening. Work in this direction is for instance the work of Limleamthong et al. (2016) They developed a new approach based on Data Envelopment Analysis (DEA) for the multi-criteria screening of molecules, according to techno-economic and environmental aspects identifying the most efficient chemicals,. This method allows establishing improvement targets for the chemicals found to be inefficient to guide research efforts in green chemistry. Establishing indicators is another avenue that is being pursued Schakel et al. (2017).In the third paper Styring et al (2022) illustrate how the alternative fuel dimethyl ether (DME) is promising to address global sustainability goals. They analyse for the first time Power-to-DME against policy requirements. This study addresses a sector that significantly contributes to atmospheric CO 2 emissions. Transport emissions grew at an annual average rate of 1.7% from 1990 to 2022, faster than any other end-use sector except for industry which grew at the same rate. To get on track with the 2050 Near Zero Emissions Scenario (NZE) CO 2 emissions must fall by more than 3% per year to 2030 (IEA50). When compared with fossil diesel, DME reduces NO x , SO x and particulate emissions (Semelsberger et al. 2006). It offers also the advantage of being easily adapted for use in conventional automotive engine systems. The analysis shows that use of DME achieves greenhouse gas (GHG) emission savings of at least 70%, meeting the criteria set up in the RED II directive.Cement is an essential material and its production and use is highly energy and materials intensive. The most common form of cement is Portland cement, about 93-97% of which consists of a material called clinker. Clinker is formed when the raw material limestone burns at a high temperature in a cement kiln generating CaO and CO 2 . Cement emissions intensity has remained relatively stable since 2018 (0.6 t CO 2 per tonne of cement produced). To get on track with the NZE Scenario, emissions must fall by an average of 3% annually through to 2030 (IEA50). Clinker substitution and adoption of green fuels will be key to put this Industry on track. In this context, in the third paper Tripathi et al.(2024) links two sectors of significant emissions, the hard to abate CO 2 emissions of the cement industry and the emissions from burning woody biomass to energy plants estimated to be 1.2 Gt CO 2 e/y, accounting for ~2.3% of global emissions Bailis et al. (2015) projected to be 2 Gt CO 2 e by 2050Booth, (2018) ) in a "end-of-waste" strategy towards a circular economy supported by the European Commission (EC (European Commission), 2011). This work exploits the ability biomass ashes to mineralise CO 2 gas and partially replace cement in mortars and shows that the additions of the different type of ashes need to be optimized for material's best performance.A potential for saving 82.5 Mt of CO 2 / 150 Mt of ash incorporated as cement replacement was estimated.Despite the promise of CCU technologies, many important sectors are not on track with NZE scenarios. This is a matter of serious concern, needing more efforts at all levels to further develop and implement these technologies.