Potassium-Promoted Limestone for Preferential Direct Hydrogenation of Carbonates in Integrated CO2 Capture and Utilization.

Integrated CO2 capture and utilization (ICCU) via the reverse water-gas shift (RWGS) reaction offers a particularly promising route for converting diluted CO2 into CO using renewable H2. Current ICCU-RWGS processes typically involve a gas-gas catalytic reaction whose efficiency is inherently limited by the Le Chatelier principle and side reactions. Here, we show a highly efficient ICCU process based on gas-solid carbonate hydrogenation using K promoted CaO (K-CaO) as a dual functional sorbent and catalyst. Importantly, this material allows ∼100% CO2 capture efficiency during carbonation and bypasses the thermodynamic limitations of conventional gas-phase catalytic processes in hydrogenation of ICCU, achieving >95% CO2-to-CO conversion with ∼100% selectivity. We showed that the excellent functionalities of the K-CaO materials arose from the formation of K2Ca(CO3)2 bicarbonates with septal K2CO3 and CaCO3 layers, which preferentially undergo a direct gas-solid phase carbonates hydrogenation leading to the formation of CO, K2CO3 CaO and H2O. This work highlights the immediate potential of K-CaO as a class of dual-functional material for highly efficient ICCU and provides a new rationale for designing functional materials that could benefit the real-life application of ICCU processes.

Phosphorus Removal from Dirty Farmyard Water by Activated Anaerobic-Digestion-Derived Biochar.

The management of anaerobic digestate is important to realize the value of the waste and enhance the whole system sustainability of anaerobic digestion. In this study, the phosphorus treatment of dirty irrigation water by biochar samples derived from digestate of anaerobic digestion were investigated. The biochars were further activated by steam activation with different duration time and KOH activation with different introducing ratios; the textural properties of biochars were optimized after activation from the aspect of biochar characterization. Notably, AD-N2 demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g-1. Besides the effect of biochar dosage on phosphorus removal, adsorption kinetics and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R2 = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH0 = 17.93 kJ mol-1) and spontaneous (ΔS = 96.24 J mol-1 K-1). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.

The Application of Biochar for CO2 Capture: Influence of Biochar Preparation and CO2 Capture Reactors.

This work investigates three types of biochar (bamboo charcoal, wood pellet, and coconut shell) for postcombustion carbon capture. Each biochar is structurally modified through physical (H2O, CO2) and chemical (ZnCl2, KOH, H3PO4) activation to improve carbon capture performance. Three methods (CO2 adsorption isotherms, CO2 fixed-bed adsorption, and thermogravimetric analysis) are used to determine the CO2 adsorption capacity. The results show that a more than 2.35 mmol·g-1 (1 bar, 298 K) CO2 capture capacity was achieved using the activated biochar samples. It is also demonstrated that the CO2 capture performance by biochar depends on multiple surface and textural properties. A high surface area and pore volume of biochar resulted in an enhanced CO2 capture capacity. Furthermore, the O*/C ratio and pore width show a negative correlation with the CO2 capture capacity of biochars.

Thermodynamic modelling of integrated carbon capture and utilisation process with CaO-based sorbents in a fixed-bed reactor.

The global emission of CO2 through fossil fuel combustion is still increasing, which is a major challenge for the international community. An integrated carbon capture and utilisation (ICCU) process with a CaO-based sorbent is a promising alternative to effectively reduce emissions. In this work, a comparative thermodynamic analysis of two CaO-based sorbents (commercial and sol-gel CaO) was performed for one cycle of ICCU. In addition, the influence of temperature was investigated from 600 to 750 °C in terms of the degree of CO2 conversion. Thermodynamic calculations were based on the actual gas composition and developed model, where heat consumption and entropy generation were calculated. The results indicate that the degree of CO2 conversion decreased from 84.6 to 41.2% and from 84.1 to 62.4% for the sol-gel and commercial material, respectively, as the temperatures increased. Furthermore, the total heat consumption during one cycle decreased with higher temperatures. The total amount of consumed heat decreased from 19.1 to 5.9 kJ/g and from 24.7 to 5.4 kJ/g for sol-gel and commercial CaO, respectively. Although commercial CaO always requires more heat during one cycle. Moreover, for both materials, the lowest generation of entropy was calculated at 650 °C with values of 9.5 and 10.1 J/g·K for the sol-gel and the commercial CaO, respectively. At all temperatures, the commercial CaO generated a greater entropy.

Integrated CO2 capture and reverse water-gas shift reaction over CeO2-CaO dual functional materials.

Achieving carbon neutrality is one of the most important tasks to meet the environmental challenges due to excessive CO2 emissions. Integrated CO2 capture and utilization (ICCU) represents an effective process for direct utilization of CO2-contained exhaust gas (e.g. flue gas), in which converting the captured CO2 into CO via reverse water-gas shift (RWGS) reaction is a promising route. The dual functional materials (DFMs), containing CO2 adsorbents and catalysts, are widely applied to achieve ICCU. The conventional active metals (Ni, Fe, etc.)-based DFMs and non-transition metal DFMs (e.g. CaO) are restricted by low CO selectivity, catalytic efficiency or CO generation in the CO2 capture step. To address the above obstructs in the application of DFMs, the metal oxides-based DFMs, MOx-CaO (M = Al, Ce, Ti or Zr), are synthesized and evaluated. The CeO2-CaO outperformed the other metal oxides-based DFMs and possessed significantly improved catalytic performance. It is found that 33% CeO2-CaO DFM displayed approximately 49% CO2 conversion and approximately 100% CO selectivity in integrated CO2 capture and reverse water-gas shift reaction (ICCU-RWGS) at 650°C, while CaO-alone only achieved approximately 20% CO2 conversion at the same condition. The surface basicity of CeO2 is revealed to contribute to the improved catalytic performance by enhancing CO2 chemisorption and activation in the hydrogenation step. Furthermore, CeO2-CaO material possessed excellent cycle stability in 20 cycles ICCU-RWGS, achieving a sustainable and high-efficient performance in CO2 conversion and CO selectivity.

Combined alkali dissolution and re-assembly approach toward ZSM-5 mesostructures with extended lifetime in cumene cracking.

The basis and contribution of mesopores created in ZSM-5 structures at different treatment conditions are systematically investigated. The results reveal that the mesopores originated from the alkali dissolution of pristine ZSM-5 are mainly intracrystalline and they contribute to excessive Brønsted acid sites, while the mesopores originated from the re-assembly of alkali dissolved aluminosilicate species possess Lewis acid sites. These ZSM-5 mesostructures showed an extended lifespan during the cracking of cumene (88.0%) in comparison to the pristine ZSM-5 (27.0%) after 460 min. The zeolite mesostructures obtained in this study could be used as a base for further design of new porous materials with desired acidic properties.