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Recently, salt-assisted pyrolyzation has been deemed an emerging and efficient method for the preparation of biochars due to its facile operation as well as its good structural and chemical properties. In this work, biochars (MBCx) are prepared by heating bamboo powders in eutectic salts (Li2CO3 + K2CO3) at 500–600 °C in the air. Multiple technologies are employed to examine the physiochemical properties of bamboo biochars. Correlations between heating temperature and structural features and carbon dioxide uptakes of bamboo biochars have been investigated. The results show that heating temperature has a significant influence on the physicochemical properties of bamboo biochars. With the elevation of the heating temperature, the defect structures of bamboo biochars gradually ascend, especially when the heating temperature reaches 600 °C. MBCx biochars visibly exceed conventional bamboo biochar prepared via pyrolyzation in a nitrogen stream free of salt addition. Pyrolysis of bamboo in eutectic salts endows biochars with higher oxygen content and more carbon defects, which likely accounts for their better CO2 capture activities. [ABSTRACT FROM AUTHOR]

[Display omitted] • First comprehensive overview on low temperature CO 2 methanation. • Overview on CO 2 methanation fundamentals, catalysts and reactor technologies. • Identified challenges and opportunities in each of the areas reviewed. • A critical process simulation result for low temperature CO 2 methanation. CO 2 utilization technologies can not only provide a pathway to reduce greenhouse gas emissions but may also enable renewable energy to be incorporated into important materials used in the society such as fuel and chemicals. Power to gas (PtG) technologies, especially Power to methane has been deemed as one of the promising pathways for the conversion of CO 2 into valuable gaseous fuel. Many reports have reviewed the academic literature related to CO 2 methanation. While the benefits of high temperature methanation for overall process efficiency are well understood, the potential for low-temperature methanation is less understood. In particular the opportunities that arise from coupling a low-temperature methanation process with low temperature hydrogen production technologies, such as PEM electrolysis, have received little attention. It is therefore considered valuable to provide a critical review of the state of the art of this technology at low temperature conditions for the interests of broader research community. In this paper we focus on the recent work around low temperature CO 2 methanation including reaction thermodynamics and kinetics, catalyst materials including supports and promoters, and suitable reactor technologies. We discuss each of these critical aspects of the technology and identify key challenges and opportunities for low temperature CO 2 methanation (methanation conducted at temperatures less than 300 °C). As part of this paper, we also present the results of an ASPEN Plus simulation study based on data available from the literature to highlight the potential energy efficiency gains of a low temperature methanation process. [ABSTRACT FROM AUTHOR]

Methane has enormous potential as a carrier for renewable H 2. The required infrastructure for a methane gas economy is readily available, and it can compete with its energy-intensive liquefied hydrogen (LH 2) counterpart. In this work, we conducted a technoeconomic analysis of the production of liquefied synthetic methane (LSM) from ambient CO 2 and renewable H 2. The process entails (1) capture of CO 2 directly from ambient air, referred to as Direct Air Capture (DAC) using an amine-based system; (2) generation of H 2 from renewable sources, (3) conversion of CO 2 and H 2 to synthetic methane; and (4) liquefaction of synthetic methane. The technoeconomic model used in this study is based on mass/material energy flow analysis and includes the economics of all processes involved. Building on our previous work, we reduced the overall capture cost for the studied scale of 0.291 t/h CO 2 production from US$557 to ~$365/tCO 2. At a scale equivalent to 1 MtCO 2 /year capture, which is the basis for production of LSM in this work, we estimated the cost of DAC to be ~$114/tCO 2. Per GJ of methane produced, the overall cost of LSM was ~$31.5/GJ, comprising around $21.7/GJ ($2.4/kg H 2) for hydrogen production, $5.6/GJ for DAC, $1.4/GJ for methanation and $2.8/GJ for methane liquefaction. The energy conversion efficiency of LSM was lower than for LH 2 , mainly due to the large amount of heat required for DAC. The levelised cost per unit of energy for LSM was lower at small scales, while the costs were the same (~$32/GJ) at a larger scale of 180 kt/year hydrogen production. Our detailed analysis provides insights into the suitability of LSM as a carbon-neutral fuel that can compete economically with LH 2. • Direct air capture (DAC) and methanation processes were integrated. • At a scale of 1 MtCO 2 /year capture, the cost of DAC was estimated ~$114/tCO 2. • Costs of LSM and LH 2 were ~$32/GJ at a scale of 180 kt/year hydrogen production. • Energy efficiency of LH 2 production was higher than that of LSM production. [ABSTRACT FROM AUTHOR]

[Display omitted] • H 2 and CO 2 mixture essential for thermal MOF-derivation of Ru0/ZrO 2. • H 2 acts by breaking down the MOF framework and by reducing Ru atoms. • CO 2 acts as a mild oxidant promoting carbon removal. • In operando powder XRD elucidated phase transition from MOF into active catalyst. Carbon Capture, Utilisation and Storage (CCUS) technologies are utilised to minimise net CO 2 emissions and hence mitigate the impact of anthropogenic emissions on the global climate. One example of CO 2 utilisation is the production of carbon-neutral methane fuel via catalytic CO 2 reduction with H 2 (methanation). Thermal activation of a metal impregnated metal-organic framework (MOF), 1 wt%Ru/UiO-66 in the presence of H 2 and CO 2 provides in situ synthesis of a highly active methanation catalyst: H 2 promotes the formation of Ru0 nanoparticles, and CO 2 behaves as a mild oxidant to remove framework carbon and promote ZrO 2 crystallisation. The nature of the active MOF-derived Ru0/ZrO 2 catalyst was studied by PXRD, TEM, and XAS, and the evolution of the parent 1 wt%Ru/UiO-66 during thermal activation monitored in operando by synchrotron PXRD. The Ru impregnated Zr-based MOF collapses on heating in H 2 and CO 2 to form an amorphous C and Zr containing phase that subsequently crystallises as tetragonal (t-) ZrO 2 nanoparticles. These t-ZrO 2 nanoparticles undergo a subsequent phase transition to the more stable monoclinic (m-) ZrO 2 polymorph. In situ activation of Ru/UiO-66 generates a highly active catalyst for CO 2 methanation by transforming the MOF precursor into a (carbon-free) crystalline t-ZrO 2 support that stabilises highly dispersed metallic Ru nanoparticles. This insight may guide the rational design of future MOF-derived catalysts. [ABSTRACT FROM AUTHOR]