The environmental sustainability of digital content consumption.

Internet access has reached 60% of the global population, with the average user spending over 40% of their waking life on the Internet, yet the environmental implications remain poorly understood. Here, we assess the environmental impacts of digital content consumption in relation to the Earth's carrying capacity, finding that currently the global average consumption of web surfing, social media, video and music streaming, and video conferencing could account for approximately 40% of the per capita carbon budget consistent with limiting global warming to 1.5 °C, as well as around 55% of the per capita carrying capacity for mineral and metal resources use and over 10% for five other impact categories. Decarbonising electricity would substantially mitigate the climate impacts linked to Internet consumption, while the use of mineral and metal resources would remain of concern. A synergistic combination of rapid decarbonisation and additional measures aimed at reducing the use of fresh raw materials in electronic devices (e.g., lifetime extension) is paramount to prevent the growing Internet demand from exacerbating the pressure on the finite Earth's carrying capacity.

The Future of Chemical Sciences is Sustainable.

Chemistry, a vital tool for sustainable development, faces a challenge due to the lack of clear guidance on actionable steps, hindering the optimal adoption of sustainability practices across its diverse facets from discovery to implementation. This Scientific Perspective explores established frameworks and principles, proposing a conciliated set of triple E priorities anchored on Environmental, Economic, and Equity pillars for research and decision making. We outline associated metrics, crucial for quantifying impacts, classifying them according to their focus areas and scales tackled. Emphasizing catalysis as a key driver of sustainable synthesis of chemicals and materials, we exemplify how triple E priorities can practically guide the development and implementation of processes from renewables conversions to complex customized products. We summarize by proposing a roadmap for the community aimed at raising awareness, fostering academia-industry collaboration, and stimulating further advances in sustainable chemical technologies across their broad scope.

Reaction Environment Design for Multigram Synthesis via Sonogashira Coupling over Heterogeneous Palladium Single-Atom Catalysts.

Single-atom heterogeneous catalysts (SACs) attract growing interest in their application in green chemistry and organic synthesis due to their potential for achieving atomic-level precision. These catalysts offer the possibility of achieving selectivity comparable to the traditionally applied organometallic complexes, while enhancing metal utilization and recovery. However, an understanding of SAC performance in organic reactions remains limited to model substrates, and their application as drop-in solutions may not yield optimal activity. Here, we investigate the previously unaddressed influence of the reaction environment, including solvent, base, cocatalyst, and ligand, on the performance of a palladium SAC in Sonogashira-Hagihara cross-couplings. By examining the effects of different solvents using the established criteria, we find that the behavior of the SAC deviates from trends observed with homogeneous catalysts, indicating a distinct interplay between heterogeneous systems and the reaction environment. Our results illustrate the satisfactory performance of SACs in cross-couplings of aryl iodides and acetylenes with electron-withdrawing and -donating groups, while the use of bromides and chlorides remains challenging. Extending the proof-of-concept stage to multigram scale, we demonstrate the synthesis of an intermediate of the anticancer drug Erlotinib. The catalyst exhibits high stability, allowing for multiple reuses, even under noninert conditions. Life-cycle assessment guides the upscaling of the catalyst preparation and quantifies the potential environmental and financial benefits of using the SAC, while also revealing the negligible impact of the PPh3 ligand and CuI cocatalyst. Our results underscore the significant potential of SACs to revolutionize sustainable organic chemistry and highlight the need for further understanding the distinct interplay between their performance and the reaction environment.

Aiming for More Sustainable Cross-Coupling Chemistry by Employing Single-Atom Catalysis on Scale.

Scaling up syntheses from mg to kg quantities is a complex endeavor. Besides adapting laboratory protocols to industrial processes and equipment and thorough safety assessments, much attention is paid to the reduction of the process' environmental impact. For processes including transition metal catalyzed steps, e.g. cross-coupling chemistry, this impact strongly depends on the identity of the metal used. As such, a key approach is the replacement of single-use with reusable heterogeneous catalysts. Transition metal single-atom heterogeneous catalysts (SAC), a novel class of catalytic materials, might exhibit all the necessary properties to step up to this task. This article shall discuss current applications of SAC in cross-coupling chemistry from the point of a process chemist and shed light on the NCCR Catalysis contribution to the field. Investigations of the stability-activity-selectivity relationship of SACs in combination with early-stage life-cycle assessments (LCA) of potential processes lay the foundation for large-scale application tailored catalyst synthesis. Ultimately, prevailing challenges are highlighted, which need to be addressed in future research.

The Environmental Feasibility of Decentralised Solar Ammonia.

Intense efforts have been devoted to developing green and blue centralised Haber-Bosch processes (gHB and bHB, respectively), but the feasibility of a decentralised and sustainable scheme has yet to be assessed. Here we reveal the conditions under which small-scale systems based on the electrocatalytic reduction of nitrogen (eN2R) powered by photovoltaic energy (NH3-leaf) could become a competitive technology in terms of environmental criteria. To this end, we calculated energy efficiency targets based on solar irradiation atlases to guide research in the incipient eN2R field. Even under this germinal state, the NH3-leaf technology would compete favourably in sunny locations relative to the business-as-usual production scenario. The disclosed sustainability potential of NH3-leaf makes it a strong ally of gHB toward a non-fossil ammonia production.

Absolute Sustainability Assessment of Flue Gas Valorization to Ammonia and Synthetic Natural Gas.

Carbon capture and utilization has gained attention to potentially curb CO2 emissions while generating valuable chemicals. These technologies will coexist with fossil analogs, creating synergies to leverage circular economy principles. In this context, flue gas valorization from power plants can assist in the transition. Here, we assessed the absolute sustainability of a simulated integrated facility producing ammonia and synthetic natural gas from flue gas from a combined-cycle natural gas power plant based in Germany, using hydrogen from three water electrolysis technologies (proton exchange membrane, alkaline, and solid oxide cells), nitrogen, and CO2. For the first time, we applied the planetary boundaries (PBs) framework to a circular integrated system, evaluating its performance relative to the safe operating space. The PB-LCA assessment showed that the alternative technologies could significantly reduce, among others, the impact on climate change and biosphere integrity when compared to their fossil counterparts, which could be deemed unsustainable in climate change. Nevertheless, these alternative technologies could also lead to burden shifting and are not yet economically viable. Overall, the investigated process could smoothen the transition toward low-carbon technologies, but its potential collateral damages should be carefully considered. Furthermore, the application of the PBs provides an appealing framework to quantify the absolute sustainability level of integrated circular systems.

Energy crisis in Europe enhances the sustainability of green chemicals.

Ammonia and methanol are essential to modern societies, but their production has been heavily reliant on natural gas, which contributes to supply disruptions and significant CO2 emissions. While low-carbon or green production routes have been extensively researched, their adoption has been hindered by higher costs, making them unsustainable. However, a recent energy crisis in Europe has created a unique opportunity to shift towards greener production technologies. Here we show that, green ammonia, produced through wind-powered water electrolysis, had the potential to outperform its fossil counterpart for six months as of December 2021, while methanol produced through CO2 capture and wind-based water electrolysis became an economically appealing alternative. With a coordinated effort from academia, industry, and policymakers, Europe can lead the grand transition towards more sustainable practices in the chemical industry.

Environmental and economic potential of decentralised electrocatalytic ammonia synthesis powered by solar energy.

Intense efforts have been devoted to developing green and blue centralised Haber-Bosch processes (gHB and bHB, respectively), but the feasibility of a decentralised and more sustainable scheme has yet to be assessed. Here we reveal the conditions under which small-scale systems (NH3-leaves) based on the electrocatalytic reduction of nitrogen (eN2R) powered by photovoltaic energy could realise a decentralised scheme competitive in terms of environmental and economic criteria. For this purpose, we calculated energy efficiency targets worldwide, providing clear values that may guide research in the incipient eN2R field. Even at this germinal stage, the NH3-leaf technology would compete favourably in sunny locations for CO2-related Earth-system processes and human health relative to the business-as-usual production scenario. Moreover, a modest 8% gain in energy efficiency would already make them outperform the gHB in terms of climate change-related impacts in the sunniest locations. If no CO2 taxation is enforced, the lowest estimated ammonia production cost would be 3 times the industrial standard, with the potential to match it provided a substantial decrease of investment costs and very high selectivity toward ammonia in eN2R are achieved. The disclosed sustainability potential of NH3-leaf makes it a strong ally of gHB toward defossilised ammonia production.

Geminal-atom catalysis for cross-coupling.

Single-atom catalysts (SACs) have well-defined active sites, making them of potential interest for organic synthesis1-4. However, the architecture of these mononuclear metal species stabilized on solid supports may not be optimal for catalysing complex molecular transformations owing to restricted spatial environment and electronic quantum states5,6. Here we report a class of heterogeneous geminal-atom catalysts (GACs), which pair single-atom sites in specific coordination and spatial proximity. Regularly separated nitrogen anchoring groups with delocalized π-bonding nature in a polymeric carbon nitride (PCN) host7 permit the coordination of Cu geminal sites with a ground-state separation of about 4 Å at high metal density8. The adaptable coordination of individual Cu sites in GACs enables a cooperative bridge-coupling pathway through dynamic Cu-Cu bonding for diverse C-X (X = C, N, O, S) cross-couplings with a low activation barrier. In situ characterization and quantum-theoretical studies show that such a dynamic process for cross-coupling is triggered by the adsorption of two different reactants at geminal metal sites, rendering homo-coupling unfeasible. These intrinsic advantages of GACs enable the assembly of heterocycles with several coordination sites, sterically congested scaffolds and pharmaceuticals with highly specific and stable activity. Scale-up experiments and translation to continuous flow suggest broad applicability for the manufacturing of fine chemicals.

Economic and Environmental Competitiveness of Ethane-Based Technologies for Vinyl Chloride Synthesis.

The synthesis of the vinyl chloride monomer (VCM), employed to manufacture poly(vinyl chloride) (PVC) plastic, primarily relies on oil-derived ethylene, resulting in high costs and carbon footprint. Natural gas-derived ethane in VCM synthesis has long been considered a transformative feedstock to lower emissions and expenses. In this work, we evaluate the environmental potential and economics of recently developed catalytic ethane chlorination technologies for VCM synthesis. We consider the ethylene-based business-as-usual (BAU) route and two different ethane-based processes evaluated at their current development level and their full potential, i.e., ideal conversion and selectivity. All routes are assessed under two temporal scenarios: present (2020) and prospective (2050). Combining process simulation and life cycle assessment (LCA), we find that catalytic ethane chlorination technologies can lower the production cost by 32% at their current development state and by 56% when considering their full potential. Though environmentally disadvantageous in the 2020 scenario, they emerge as more sustainable alternatives to the BAU in the 2050 scenario, reducing the carbon footprint of VCM synthesis by up to 26% at their current state and up to 58% at their full potential. Going beyond VCM synthesis, our results highlight prospective LCA as a powerful tool for assessing the true environmental implications of emerging technologies under more decarbonized future energy scenarios.

Microalgae Biofuel for a Heavy-Duty Transport Sector within Planetary Boundaries.

In this contribution, we study the extent to which 68 scenarios for microalgae biofuels could help the heavy-duty transport sector operate within planetary boundaries. The proposed scenarios are built considering a range of alternative configurations based on three types of fuel production processes (i.e., transesterification, hydrodeoxygenation, and hydrothermal liquefaction), different carbon sources (such as natural gas power plants and direct air capture), byproduct treatments, and two electricity mixes. Our results reveal that microalgae biofuels could significantly reduce the environmental and human health impacts of the business-as-usual (fossil-based) heavy-duty transport sector. Moreover, relative to standard biofuels that show large land-use requirements, we find that microalgae biofuels also decrease the damage on biosphere integrity substantially. Notably, pathways resorting to hydrodeoxygenation of microalgae oil and direct air capture and carbon storage could reduce the current impact induced globally on climate change by the heavy transport by 77%, while attaining six-fold reductions in biosphere integrity impacts, both relative to conventional biofuels.

Low-carbon diets can reduce global ecological and health costs.

Potential external cost savings associated with the reduction of animal-sourced foods remain poorly understood. Here we combine life cycle assessment principles and monetarization factors to estimate the monetary worth of damage to human health and ecosystems caused by the environmental impacts of food production. We find that, globally, approximately US$2 of production-related external costs were embedded in every dollar of food expenditure in 2018-corresponding to US$14.0 trillion of externalities. A dietary shift away from animal-sourced foods could greatly reduce these 'hidden' costs, saving up to US$7.3 trillion worth of production-related health burden and ecosystem degradation while curbing carbon emissions. By comparing the health effects of dietary change from the consumption versus the production of food, we also show that omitting the latter means underestimating the benefits of more plant-based diets. Our analysis reveals the substantial potential of dietary change, particularly in high and upper-middle-income countries, to deliver socio-economic benefits while mitigating climate change.

Global Sensitivity Analysis in Life-Cycle Assessment of Early-Stage Technology using Detailed Process Simulation: Application to Dialkylimidazolium Ionic Liquid Production.

The ability to assess the environmental performance of early-stage technologies at production scale is critical for sustainable process development. This paper presents a systematic methodology for uncertainty quantification in life-cycle assessment (LCA) of such technologies using global sensitivity analysis (GSA) coupled with a detailed process simulator and LCA database. This methodology accounts for uncertainty in both the background and foreground life-cycle inventories, and is enabled by lumping multiple background flows, either downstream or upstream of the foreground processes, in order to reduce the number of factors in the sensitivity analysis. A case study comparing the life-cycle impacts of two dialkylimidazolium ionic liquids is conducted to illustrate the methodology. Failure to account for the foreground process uncertainty alongside the background uncertainty is shown to underestimate the predicted variance of the end-point environmental impacts by a factor of two. Variance-based GSA furthermore reveals that only few foreground and background uncertain parameters contribute significantly to the total variance in the end-point environmental impacts. As well as emphasizing the need to account for foreground uncertainties in LCA of early-stage technologies, these results illustrate how GSA can empower more reliable decision-making in LCA.

Absolute environmental sustainability assessment of renewable dimethyl ether fuelled heavy-duty trucks.

In recent years, liquid fuels from renewable carbon that can replace fossil ones with minimal infrastructure changes have attracted increasing interest in decarbonising the heavy-duty long-haul sector. Here we focus on dimethyl ether (DME), a promising alternative to diesel due to its high cetane number, oxygen content, and more efficient and cleaner propulsion that results in low particulate matter and sulphur oxide emissions. Going well beyond previous studies that quantified the environmental impact of DME, often in terms of global warming, here we evaluate DME use in heavy-duty trucks in the context of seven planetary boundaries, all essential for maintaining the Earth's stability. Focusing on several scenarios differing in the feedstock origin, we find that routes based on fossil carbon, either in the form of coal, natural gas, or captured CO2 from fossil plants, would increase the greenhouse gas emissions relative to the business-as-usual. Only scenarios based on renewable carbon could reduce the impacts on climate change, while hydrogen from biomass gasification coupled with carbon capture and storage (CCS) and DME from biomass gasification with CCS could enable an environmentally sustainable operation within all the planetary boundaries. Overall, our work opens up new avenues for the environmental assessment of fuels considering the finite capacity of the Earth system to guide research and policy-making more sensibly.

Environmental Sustainability Assessment of Hydrogen from Waste Polymers.

The rising demand for single-use polymers calls for alternative waste treatment pathways to ensure a circular economy. Here, we explore hydrogen production from waste polymer gasification (wPG) to reduce the environmental impacts of plastic incineration and landfilling while generating a valuable product. We assess the carbon footprint of 13 H2 production routes and their environmental sustainability relative to the planetary boundaries (PBs) defined for seven Earth-system processes, covering H2 from waste polymers (wP; polyethylene, polypropylene, and polystyrene), and a set of benchmark technologies including H2 from natural gas, biomass, and water splitting. Our results show that wPG coupled with carbon capture and storage (CCS) could reduce the climate change impact of fossil-based and most electrolytic routes. Moreover, due to the high price of wP, wPG would be more expensive than its fossil- and biomass-based analogs but cheaper than the electrolytic routes. The absolute environmental sustainability assessment (AESA) revealed that all pathways would transgress at least one downscaled PB, yet a portfolio was identified where the current global H2 demand could be met without transgressing any of the studied PBs, which indicates that H2 from plastics could play a role until chemical recycling technologies reach a sufficient maturity level.

Reaction-Induced Formation of Stable Mononuclear Cu(I)Cl Species on Carbon for Low-Footprint Vinyl Chloride Production.

Copper catalysts are attractive candidates for Hg-free vinyl chloride monomer (VCM) production via acetylene hydrochlorination due to their non-toxic nature and high stability. However, the optimal architecture for Cu-based catalysts at the nanoscale is not yet fully understood. To address this gap, the metal precursor and the annealing temperature are modified to prepare copper nanoparticles or single atoms, either in chlorinated or ligand-free form, on an unmodified carbon support. Evaluation in the reaction reveals a remarkable convergence of the performance of all materials to the stable VCM productivity of the single-atom catalyst. In-depth characterization by advanced microscopy, quasi in situ and operando spectroscopy, and simulations uncover a reaction-induced formation of low-valent, single atom Cu(I)Cl site motif, regardless of the initial nanostructure. Various surface oxygen groups promote nanoparticle redispersion by stabilizing single-atom CuClx species. The anchoring site structure does not strongly influence the acetylene adsorption energy or the crucial role they play in stabilizing key reaction intermediates. A life-cycle assessment demonstrates the potential environmental benefits of copper catalysts over state-of-the-art alternatives. This work contributes to a better understanding of optimal metal speciation and highlights the sustainability of Cu-based catalysts for VCM production.

Economic and Environmental Performance of an Integrated CO2 Refinery.

The consequences of global warming call for a shift to circular manufacturing practices. In this context, carbon capture and utilization (CCU) has become a promising alternative toward a low-emitting chemical sector. This study addresses for the first time the design of an integrated CO2 refinery and compares it against the business-as-usual (BAU) counterpart. The refinery, which utilizes atmospheric CO2, comprises three synthesis steps and coproduces liquefied petroleum gas, olefins, aromatics, and methanol using technologies that were so far studied decoupled from each other, hence omitting their potential synergies. Our integrated assessment also considers two residual gas utilization (RGU) designs to enhance the refinery's efficiency. Our analysis shows that a centralized cluster with an Allam cycle for RGU can drastically reduce the global warming impact relative to the BAU (by ≈135%) while simultaneously improving impacts on human health, ecosystems, and resources, thereby avoiding burden-shifting toward human health previously observed in some CCU routes. These benefits emerge from (i) recycling CO2 from the cycle, amounting to 11.2% of the total feedstock, thus requiring less capture capacity, and (ii) reducing the electricity use while increasing heating as a trade-off. The performance of the integrated refinery depends on the national grid, while its high cost relative to the BAU is due to the use of expensive electrolytic H2 and atmospheric CO2 feedstock. Overall, our work highlights the importance of integrating CCU technologies within chemical clusters to improve their economic and environmental performance further.

Trade-offs between Sustainable Development Goals in carbon capture and utilisation.

Carbon capture and utilisation (CCU) provides an appealing framework to turn carbon emissions into valuable fuels and chemicals. However, given the vast energy required to activate the CO2 molecule, CCU may have implications on sustainable development that are still poorly understood due to the narrow scope of current carbon footprint-oriented assessments lacking absolute sustainability thresholds. To bridge this gap, we developed a power-chemicals nexus model to look into the future and understand how we could produce 22 net-zero bulk chemicals of crucial importance in a sustainable manner by integrating fossil, CCU routes and power technologies, often assessed separately. We evaluated the environmental performance of these technologies in terms of their contribution to 5 Sustainable Development Goals (SDGs), using 16 life cycle assessment metrics and 9 planetary boundaries (PB) to quantify and interpret the impact values. We found that fossil chemicals could hamper the attainment of SDG 3 on good health and well-being and SDG 13 on climate change. CCU could help meet SDG 13 but would damage other SDGs due to burden-shifting to human health, water scarcity, and minerals and metals depletion impacts. The collateral damage could be mitigated by judiciously combining fossil and CCU routes with carbon-negative power sources guided by optimisation models incorporating SDGs-based performance criteria explicitly. Our work highlights the importance of embracing the SDGs in technology development to sensibly support the low-carbon energy and chemicals transition.

Net-zero transition of the global chemical industry with CO2-feedstock by 2050: feasible yet challenging.

Carbon capture, utilization and storage (CCUS) have been projected by the power and industrial sectors to play a vital role towards net-zero greenhouse gas emissions. In this study, we aim to explore the feasibility of a global chemical industry that fully relies on CO2 as its carbon source in 2050. We project the global annual CO2 demand as chemical feedstock to be 2.2-3.1 gigatonnes (Gt), well within the possible range of supply (5.2-13.9 Gt) from the power, cement, steel, and kraft pulp sectors. Hence, feedstock availability is not a constraint factor for the transition towards a fully CO2-based chemical industry on the global basis, with the exception of few regions that could face local supply shortages, such as the Middle East. We further conduct life cycle assessment to examine the environmental benefits on climate change and the trade-offs of particulate matter-related health impacts induced by carbon capture. We conclude that CO2 captured from solid biomass-fired power plants and kraft pulp mills in Europe would have the least environmental and health impacts, and that India and China should prioritize low-impact regional electricity supply before a large-scale deployment of CCUS. Finally, two bottom-up case studies of China and the Middle East illustrate how the total regional environmental and health impacts from carbon capture can be minimized by optimizing its supply sources and transport, requiring cross-sectoral cooperation and early planning of infrastructure. Overall, capture and utilization of unabatable industrial waste CO2 as chemical feedstock can be a feasible way for the net-zero transition of the industry, while concerted efforts are yet needed to build up the carbon-capture-and-utilization value chain around the world.

Bayesian Symbolic Learning to Build Analytical Correlations from Rigorous Process Simulations: Application to CO2 Capture Technologies.

Process modeling has become a fundamental tool to guide experimental work. Unfortunately, process models based on first principles can be expensive to develop and evaluate, and hard to use, particularly when convergence issues arise. This work proves that Bayesian symbolic learning can be applied to derive simple closed-form expressions from rigorous process simulations, streamlining the process modeling task and making process models more accessible to experimental groups. Compared to conventional surrogate models, our approach provides analytical expressions that are easier to communicate and manipulate algebraically to get insights into the process. We apply this method to synthetic data obtained from two basic CO2 capture processes simulated in Aspen HYSYS, identifying accurate simplified interpretable equations for key variables dictating the process economic and environmental performance. We then use these expressions to analyze the process variables' elasticities and benchmark an emerging CO2 capture process against the business as usual technology.