Atom efficiency, defined here as catalytic output per unit total noble-metal mass rather than per exposed atom, is a decisive design target for noble-metal-lean CO 2 methanation. We show that it can be tuned by controlling the chemistry of just the outermost atomic layers of the support. Ru/CeO 2 catalysts with an ultra-low nominal Ru loading (0.15 wt.%) were prepared on morphology-controlled ceria (nanocubes and nanorods) whose topmost layers were modified with Zr or Pr. Nanocubes outperformed nanorods despite their sixfold lower surface area, suggesting a morphology-dependent catalytic effect with a probable crystallographic contribution in the ultra-dispersed limit, beyond textural properties alone. Our results challenge the prevailing oxygen-vacancy paradigm: although Pr markedly increased reducibility and vacancy abundance, it consistently suppressed activity, reducing CO 2 conversion by up to sixfold at low temperature. Vacancy-related indicators therefore do not appear to be reliable activity descriptors here. Performance instead appears to be governed by the local chemical environment of the Ru sites: an intimate, reducible metal-support interface combined with a predominance of weak basic sites. Pr appears to disrupt this interface and to strengthen CO 2 binding, which plausibly explains its detrimental effect on turnover. Guided by these principles, the Ru/ZrCeO 2 nanocube catalyst reaches ca. 65 mol CO 2 ·g Ru –1 ·h –1 with >95% CH 4 selectivity, a high Ru-mass-normalized activity compared with previously reported Ru-based catalysts of far higher metal content, although differing reaction conditions limit direct comparison. These findings point to local interfacial chemistry, rather than bulk reducibility, dispersion, or oxygen-vacancy density, as a key descriptor of atom efficiency.
Growing concern over CO 2 emissions from industrial exhaust and fossil fuel combustion renders efficient, cost-effective CO 2 capture imperative for net-zero hard-to-abate industries. Rotating Packed Beds (RPBs), as process intensification equipment with high gas–liquid mass-transfer (MT) efficiency, are promising alternatives to traditional packed columns in amine-based absorption. Modeling the reaction-diffusion process within droplets formed at high rotational speeds in an RPB can play an effective role in predicting absorption performance and designing intensified MT equipment like RPB. The aim of this research is to develop a steady-state droplet-scale model for RPB-based absorption by DETA solvent. Concentration profiles of CO 2 and DETA along the radial depth of the droplet were assessed, and the impact of rotational speed on absorption performance (MT flux) was evaluated. Furthermore, the effects of these variables on the enhancement factor were analyzed to investigate the influence of the reaction on CO 2 absorption within the droplet. To provide insight into the reaction mechanism in the amine-based chemical absorption process, the distribution of amine and water in the reaction as a function of solvent concentration was investigated. Finally, the reaction regime diagram was constructed to determine the prevailing regime in chemical absorption, and the outcomes were consistent with the pseudo-first-order assumption.
This study evaluated the environmental performance of a novel integrated biorefinery that converts household food waste, one of the largest urban organic waste streams, into high-purity n-butyric acid (BA). The process comprised hydrothermal pretreatment, lactic acid fermentation, and BA fermentation. Two downstream recovery strategies were compared, namely adsorptive separation using zeolite (Scenario 1) and extractive distillation (Scenario 2). A gate-to-gate life cycle assessment and hotspot analysis were conducted using ReCiPe 2016 based on Aspen Plus simulations and detailed process equipment design. Adsorptive separation demonstrated superior environmental performance compared with extractive distillation across all impact categories. At 85% recovery, Scenario 1 required 0.113 MWh/t of electricity and 0.234 MWh/t of heat, compared with 0.261 MWh/t and 3.08 MWh/t, respectively, for Scenario 2, resulting in 29-97% lower endpoint damages. Accordingly, human health, ecosystem, and resource damages associated with product recovery decreased from 3.096 × 10⁻³ to 1.346 × 10⁻³ DALY, from 14.188 × 10⁻⁶ to 10.042 × 10⁻⁶ species·yr, and from 182 to 24 USD2013, respectively. Increasing BA recovery from 85% to 99% reduced endpoint damages by 13–22% in Scenario 2, whereas the corresponding reductions in Scenario 1 were <2%. The results identified BA fermentation as the dominant contributor, accounting for 70–75% of total environmental impacts, while nutrient inputs were responsible for 95–97% of fermentation-related impacts. These findings highlight nutrient management as the primary opportunity for reducing the environmental footprint of food-waste-based BA production and improving the sustainability of urban food waste valorization systems.
Hydrodeoxygenation (HDO) is a key upgrading technology for biomass-derived bio-oils, but its dependence on high-pressure external hydrogen limits its economic and environmental sustainability. Hydrogen-free HDO has recently emerged as an appealing alternative by exploiting water as the hydrogen source, although the design of suitable multifunctional catalysts remains a major challenge. Herein, the influence of catalyst support on H2-free HDO was systematically investigated using 2 wt.% Ru catalysts supported on activated carbon (AC), TiO2, ZSM5 zeolite, Mg-Al hydrotalcite (HT), and CeO2-Al2O3 mixed oxide. Catalytic performance was correlated with structural, textural, redox and acid-base properties through a comprehensive characterisation analysis. Ru/AC exhibited the highest activity, achieving 75 % guaiacol conversion and a phenol yield of 46 %, whereas Ru/ZSM5 showed high conversion with catechol as the predominant product. The superior performance of Ru/AC was attributed to its high surface area, excellent Ru dispersion and metal-support interaction. Conversely, stronger metal-support interactions and limited Ru reducibility resulted in inferior catalytic performance for CeO2-Al2O3 and hydrotalcite-supported catalysts. Although Ru/AC suffered deactivation upon recycling because of particle sintering and surface coverage, this work identifies the key catalyst descriptors governing hydrogen-free HDO and provides rational design guidelines for the next-generation of multifunctional catalysts for sustainable biofuel production within the CLEVER-FUEL approach.
Growing concern over CO2 emissions from industrial exhaust and fossil fuel combustion renders efficient, cost-effective CO2 capture imperative for net-zero hard-to-abate industries. Rotating Packed Beds (RPBs), as process intensification equipment with high gas–liquid mass-transfer (MT) efficiency, are promising alternatives to traditional packed columns in amine-based absorption. Modeling the reaction-diffusion process within droplets formed at high rotational speeds in an RPB can play an effective role in predicting absorption performance and designing intensified MT equipment like RPB. The aim of this research is to develop a steady-state droplet-scale model for RPB-based absorption by DETA solvent. Concentration profiles of CO2 and DETA along the radial depth of the droplet were assessed, and the impact of rotational speed on absorption performance (MT flux) was evaluated. Furthermore, the effects of these variables on the enhancement factor were analyzed to investigate the influence of the reaction on CO2 absorption within the droplet. To provide insight into the reaction mechanism in the amine-based chemical absorption process, the distribution of amine and water in the reaction as a function of solvent concentration was investigated. Finally, the reaction regime diagram was constructed to determine the prevailing regime in chemical absorption, and the outcomes were consistent with the pseudo-first-order assumption.
