Radical-dominated reaction of CO–NO on a CaFe2O4 surface in sintering flue gas recirculation

Catalytic reduction of nitrogen monoxide using iron-nickel oxygen carriers derived from electroplating sludge: Novel method for the collaborative emission decrease of polluting gases

The valorization of electroplating sludge (ES) for high added value presents greater economic and environmental benefits than conventional treatment methods such as thermal processing, solidification, and landfill. Inspired by the mechanism of chemical looping combustion (CLC), this study developed a novel cost-effective method for denitrification by preparing FeNi-OCs from ES to achieve the synergistic reduction of CO and NO emissions. The phase structure, micromorphology, and valence state changes of the FeNi-OC catalyst during the CO-catalyzed reduction of NO and the pathway for catalytic denitrification using FeNi-OCs were analyzed. Results showed that CO could reduce FeNi-OCs to FeNi, and the reduced FeNi was subsequently oxidized back to FeNi-OCs by NO, a process analogous to CLC. During experiments, the simultaneous consumption of CO and NO gases was observed at 350 °C. This phenomenon was highly pronounced at 600 °C, where the CO and NO concentrations decreased from initial values of 8550 and 470 ppm, respectively, to 6719 and 0 ppm, respectively, with conversion rates of 21.41 % and 100 %, respectively. Hence, synergistic emission reduction was achieved. Further experiments also indicated that the addition of 1.5 % ES during iron ore sintering could substantially reduce the CO and NO concentrations in the sintering flue gas from 1268.32 and 244.81 ppm, respectively, to 974.51 and 161.11 ppm, respectively.

Catalytic removal of gaseous pollutant NO using CO: Catalyst structure and reaction mechanism

Carbon monoxide (CO) has recently been considered an ideal reducing agent to replace NH3 in selective catalytic reduction of NOx (NH3-SCR). This shift is particularly relevant in diesel engines, coal-fired industry, the iron and steel industry, of which generate substantial amounts of CO due to incomplete combustion. Developing high-performance catalysts remain a critical challenge for commercializing this technology. The active sites on catalyst surface play a crucial role in the various microscopic reaction steps of this reaction. This work provides a comprehensive overview and insights into the reaction mechanism of active sites on transition metal- and noble metal-based catalysts, including the types of intermediates and active sites, as well as the conversion mechanism of active molecules or atoms. In addition, the effects of factors such as O2, SO2, and alkali metals, on NO reduction by CO were discussed, and the prospects for catalyst design are proposed. It is hoped to provide theoretical guidance for the rational design of efficient CO selective catalytic denitration materials based on the structure-activity relations.

Emission reduction of PCDD/Fs by flue gas recirculation and activated carbon in the iron ore sintering

One of the main sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the environment is the sintering of iron ore. Both flue gas recirculation (FGR) and activated carbon (AC), which have the impact of decreasing both PCDD/Fs and conventional pollutants (NOx, SO2, etc.), are significant technologies for the abatement of PCDD/Fs from the sintering exhaust gas. This work involved the first measurement of PCDD/Fs emissions during FGR and a thorough analysis of the impact of PCDD/Fs reduction following the coupling of FGR and AC technologies. According to the measured data, the ratio of PCDFs to PCDDs in the sintered flue gas was 6.8, indicating that during the sintering process, the PCDD/Fs were primarily produced by de novo synthesis. Further investigation revealed that FGR initially removed 60.7% of PCDD/Fs by returning it to the high temperature bed, and AC further removed 95.2% of the remaining PCDD/Fs through physical adsorption. While AC is better at removing PCDFs and can efficiently remove tetra-to octa-chlorinated homologs, FGR is more effective at removing PCDDs and has higher removal efficiency for hexa-to octa-chlorinated PCDD/Fs. Together, they complement each other with a removal rate of 98.1%. The study's findings are instructional for the process design of combining FGR and AC technologies to reduce PCDD/Fs in the sintered flue gas.

Experimental study of the effect of CO2 on temperature and soot volume fraction in C2H4/air co-flow laminar diffusion flame

The threat of global warming caused by greenhouse gases such as CO2 to the environment is one of the most intractable challenges. The capture and utilization of CO2 are essential to reduce its emission and achieve the goal of being carbon neutral, in which CO2-diluted combustion is an efficient carbon capture technology. In this research, the effects of CO2 addition in the fuel side (CO2-F), oxidizer side (CO2-O) and both sides (CO2-F/O) on temperature and soot formation in C2H4/air laminar co-flow diffusion flames were researched. The flame images were measured by a complementary metal-oxide-semiconductor (CMOS) imaging equipment. The two-dimensional distributions of temperature and soot volume fraction in C2H4/air laminar co-flow diffusion flames were measured employing the inverse Abel transform. The results demonstrated that the effect of amount variation of CO2-F on the decrease of flame temperature was enhanced by the CO2-O. The reduction in peak flame temperature was 4 K in the CO2-F cases, while the reduction in peak flame temperature was 83 K in the CO2-F/O cases. The soot formation was suppressed significantly by the effects of CO2-F/O. Compared with the CO2-F cases, the reductions in peak soot volume fraction were 22.5% and 23.5% in the CO2-F/O cases. The suppression effect of amount variation of the CO2-F on soot formation became more significant with the increase of flame height. The reductions in peak soot volume fractions were 0.3%, 3.07% and 6.38% at the flame heights of 20 mm, 30 mm and 40 mm in the CO2-F cases, and the corresponding reductions were 4.92%, 5.2% and 16% in the CO2-F/O cases, respectively.

The exploration of metal-free catalyst g-C3N4 for NO degradation

We propose a new metal-free scheme of the reaction between the molecules CO and NO on a g-C₃N₄ monolayer. We first investigate the electronic properties of the related molecules CO, NO, N₂, and CO₂ adsorbed g-C₃N₄ systems, and then figure out the possible reaction pathways. It is shown that all the molecules will be physisorbed above the triangular cavity. Also, we find the NO binding on g-C₃N₄ is stronger than CO. The NO dissociation will be the rate-determining step of the reaction, and the formation of NCO· intermediate will play a critical role for the reaction process. This research presents a new route of applying g-C₃N₄ as a catalyst in the NO catalytic degradation reaction.