Research on carbon dioxide capture materials used for carbon dioxide capture, utilization, and storage technology: a review

In recent years, climate change has increasingly become one of the major challenges facing mankind today, seriously threatening the survival and sustainable development of mankind. Dramatically increasing carbon dioxide concentrations are thought to cause a severe greenhouse effect, leading to severe and sustained global warming, associated climate instability and unwelcome natural disasters, melting glaciers and extreme weather patterns. The treatment of flue gas from thermal power plants uses carbon capture, utilization, and storage (CCUS) technology, one of the most promising current methods to accomplish significant CO2 emission reduction. In order to implement the technological and financial system of CO2 capture, which is the key technology of CCUS technology and accounts for 70-80% of the overall cost of CCUS technology, it is crucial to create more effective adsorbents. Nowadays, with the development and application of various carbon dioxide capture materials, it is necessary to review and summarize carbon dioxide capture materials in time. In this paper, the main technologies of CO2 capture are reviewed, with emphasis on the latest research status of CO2 capture materials, such as amines, zeolites, alkali metals, as well as emerging MOFs and carbon nanomaterials. More and more research on CO2 capture materials has used a variety of improved methods, which have achieved high CO2 capture performance. For example, doping of layered double hydroxides (LDH) with metal atoms significantly increases the active site on the surface of the material, which has a significant impact on improving the CO2 capture capacity and performance stability of LDH. Although many carbon capture materials have been developed, high cost and low technology scale remain major obstacles to CO2 capture. Future research should focus on designing low-cost, high-availability carbon capture materials.

Effect of NO2 on N2 O production and NOx emission reduction in NH3 Selective Catalytic Reduction

With the introduction of increasingly strict emission regulations, reducing nitrogen oxide (NOx ) emissions and nitrous oxide (N2 O) production from diesel engines have become the focus of research. At high temperature, the reaction of NO2 in the catalyst generates the intermediate product NH4 NO3 , which first crystallizes below 300 °C. These crystals tend to block the pores and inhibit the reaction. Subsequently, N2 O is produced through the decomposition of NH4 NO3 , leading to additional pollution. Therefore, the concentration of NO2 has a direct impact on both the NOx conversion efficiency and the generation of N2 O, requiring consideration of the optimal proportion of NO2 in SCR. Considering these two factors, it is concluded that the optimal amount of NO2 varies with temperature. To improve the NOx conversion rate of the Cu-SSZ-13 catalyst at low temperatures and reduce N2 O generation, the optimal NO2 ratio of the Cu-SSZ-13 catalyst under various operating conditions is studied using numerical simulations. As the temperature rises, the optimal NO2 /NOx ratio first increases and then decreases. Under the optimal NO2 /NOx ratio, the NOx conversion rate significantly increases, while N2 O generation decreases considerably. The optimal NO2 /NOx ratio also provides suggestions for the optimization of the DOC-DPF-DCR system.

Rapid Ozone Decomposition over Water-activated Monolithic MoO3 /Graphdiyne Nanowalls under High Humidity

Catalytic ozone (O3 ) decomposition at high relative humidity (RH) remains a great challenge due to the catalysts poison and deactivation under high humidity. Here, we firstly elaborate the role of water activation and the corresponding mechanism of the promoted O3 decomposition over the three-dimensional monolithic molybdenum oxide/graphdiyne (MoO3 /GDY) catalyst. The O3 decomposition over MoO3 /GDY reaches up to 100 % under high humid condition (75 % RH) at room temperature, which is 4.0 times as high as that of dry conditions, significantly surpasses other carbon-based MoO3 materials(≤7.1 %). The sp-hybridized carbon in GDY donates electrons to MoO3 along the C-O-Mo bond, facilitating water activation to form hydroxyl species. As a result, hydroxyl species dissociated from water act as new active sites, promoting the adsorption of O3 and the generation of new intermediate species (hydroxyl ⋅OH and superoxo ⋅O2 - ), which significantly lowers the energy barriers of O3 decomposition (0.57 eV lower than dry conditions).

Study on the Emission Characteristics of Urban Buses at Different Emission Standards Fueled with Biodiesel Blends

Biodiesel is a promising clean and alternative fuel that can meet the demand of energy saving and environmental protection. In this study, the effects of biodiesel blends on the gaseous and particulate emission characteristics of China-III, IV, and V urban buses were investigated based on a heavy chassis dynamometer. The results showed that the biodiesel blend resulted in a reduction in CO, THC, PN, and PM emission but an increase in the NOx and CO₂ emission, and the effects were enhanced with the biodiesel ratio, which also depended on the bus speed. Simultaneously, the emission standards of buses had an obvious effect on the emissions and changed the effect of biodiesel on the emissions. A higher emission standard of the bus highlighted the effect of biodiesel on the emission. From China-III to China-IV to China-V buses, the comprehensive changes produced by B5 in the emissions increased from 5.57 to 6.78 to 6.83%, while for B10, a significant increase in the changes was obtained, reaching 12.98, 14.68, and 15.02%, respectively, for the three emission stage buses.

Experimental Study on Entrainment Characteristics of High-Pressure Methane Free Jet

Entrainment occurs during the high-pressure gas jet process, which is crucial for a natural gas direct injection engine. This study presents an experimental investigation on the high-pressure methane jet from one single-hole injector and proposes a method to obtain the entrainment mass flow rate based on kinetic energy conservation. The entrainment is related to three variables, i.e., spring plate moving distance Δx, gas jet mass at the nozzle outlet m _n, and gas jet velocity u ₁. A spring-set test rig is built to measure the spring plate moving distance Δx, and the schlieren method is adopted to test the gas jet velocity u ₁ based on a constant-volume bomb (CVB) optical test rig; finally, the weight method is used to obtain the methane gas jet mass at the nozzle outlet m _n. This combined measuring method is verified to be valid in the near field to the nozzle. The results show that the methane jet mass flow rate gradually increases along the jet direction and has a two-zone entrainment process. Zone I: near field (Lr < 10), the methane jet mass flow rate linearly increases up to the maximum; in the nozzle exit field (Lr < 1), it is conserved, and no entrainment occurs. Zone II: far field (Lr ≥ 10), the jet mass flow rate maintains the maximum, and the entrainment becomes saturated with a saturation value larger than the initial value at the nozzle outlet. The entrainment rate experiences three stages, linearly increasing in stage I and early stage II but not in late stage II and stage III. The methane injection pressure causes great effects on the mass flow rate and entrainment. As the injection pressure increases, the methane jet mass flow rate increases linearly, but the entrainment rate decreases.

Development of Natural Gas Chemical Kinetic Mechanisms and Application in Engines: A Review

In this paper, the brief development of chemical kinetic modeling of natural gas is discussed, with emphasis on the development of chemical kinetic mechanisms describing fuel oxidation. The addition of ethane and/or propane to natural gas not only decreases the ignition delay times but also increases flame speeds. Thus, the mixture of methane, ethane, and propane rather than bare methane obtains more accurate predictions for the combustion and emission characteristics of natural gas. This paper also evaluates different comprehensive mechanisms employed for natural gas engines and pointed out their advantages and disadvantages, giving guidance for the selection of mechanisms during the development of natural gas engines.

Soot combustion over CeO2 catalyst: the influence of biodiesel impurities (Na, K, Ca, P) on surface chemical properties

This work assessed the impact of biodiesel impurities on CeO2 catalyst for soot combustion via soot-TPO experiments. The results showed that Na- and K-doped catalysts were assisted for soot combustion, while Ca- and P-doped catalysts had a negative effect. N2 adsorption-desorption and XRD results indicated that doping biodiesel impurities led to smaller surface area by blocking small pores. Surface chemical properties are suggested as major reasons for promoting soot combustion by means of XPS, H2-TPR, and O2-TPD. Na- and K-doped catalysts showed stronger redox ability and surface lattice oxygen mobility, poorly for Ca- and P-doped catalysts. Interestingly, a large number of surface oxygen species were observed on P-doped catalyst and it enhanced the ignition of bio soot. In the presence of NO, surface chemical properties including NOx storage/release capacity and NO oxidation ability were characterized by NO-adsorption DRIFTS, NO-TPO and NOx-desorption DRIFTS, alkali-doped catalyst with excellent NOx storage capacity that can release active oxygen species and gaseous NO2 accelerate heterogeneous soot combustion, and the poor NO conversion ability to NO2 that weakens the promotion effect of soot combustion. Particularly in the existence of P, the promotion effect of soot elimination in NO + O2 was further weakened by the reason of poor NOx storage capacity and NO oxidation ability.