A Low-Noble-Metal Ru@CoMn2O4 Spinel Catalyst for the Efficient Oxidation of Propane.

Noble metals have become a research hotspot for the oxidation of light alkanes due to their low ignition temperature and easy activation of C-H; however, sintering and a high price limit their industrial applications. The preparation of effective and low-noble-metal catalysts still presents profound challenges. Herein, we describe how a Ru@CoMn2O4 spinel catalyst was synthesized via Ru in situ doping to promote the activity of propane oxidation. Ru@CoMn2O4 exhibited much higher catalytic activity than CoMn2O4, achieving 90% propane conversion at 217 °C. H2-TPR, O2-TPD, and XPS were used to evaluate the catalyst adsorption/lattice oxygen activity and the adsorption and catalytic oxidation capacity of propane. It could be concluded that Ru promoted synergistic interactions between cobalt and manganese, leading to electron transfer from the highly electronegative Ru to Co2+ and Mn3+. Compared with CoMn2O4, 0.1% Ru@CoMn2O4, with a higher quantity of lattice oxygen and oxygen mobility, possessed a stronger capability of reducibility, which was the main reason for the significant increase in the activity of Ru@CoMn2O4. In addition, intermediates of the reaction between adsorbed propane and lattice oxygen on the catalyst were monitored by in situ DRIFTS. This work highlights a new strategy for the design of a low-noble-metal catalyst for the efficient oxidation of propane.

Changes of Nitrate Activity and Byproduct Distribution Characteristics for Synergistic NOx and Dioxin Abatement over V2O5/AC Catalyst.

The simultaneous removal of NOx and dioxins has been considered an economical and effective technology of controlling multipollutant flue gas in the context of "carbon peaking and carbon neutrality". However, this technology has not yet been implemented in practical situations, because the interactive relationship between the selective catalytic reduction (SCR) reaction and dioxin catalytic oxidation lacks a deep understanding, especially on a carbon-based catalyst. In this research, the influence of NO and NH3 on the oxidation characteristics and byproducts distribution of dibenzofuran (DBF) was studied on V2O5/AC catalyst. Results indicated that NH3 has a stronger inhibition effect for DBF catalytic oxidation than NO due to obvious competitive adsorption between NH3 and DBF on the V2O5/AC catalyst. In addition, although both NO and NH3 inhibit the complete degradation of DBF, their effects on the byproduct distribution are not consistent. NO primarily affects the level of oxygen-containing byproducts, while NH3 primarily affects the level of alkane byproducts. Furthermore, the SCR reaction activity demonstrated a reduction when DBF was present. The occupation of V2O5 sites by DBF and its oxidizing intermediates has hindered the production of monodentate nitrate and the reactivity of bridged nitrate, resulting in a decrease in SCR activity via the L-H mechanism. This work aims to provide theoretical guidance for simultaneous removal of NOx and dioxins in industrial fumes.

Unravelling the impacts of sulfur dioxide on dioxin catalytic decomposition on V2O5/AC catalysts.

Dioxins are high chlorine, toxic, and persistent organic pollutants that exert significant pressure on both human and the environment. From the analysis of current pollutant removal of the whole life cycle, such as integrated removal of NOx, SO2 and dioxins in a system, the dioxins oxidation activity as well as the distribution of oxidation products in the presence of SO2 are still a challenge. In this study, dibenzofuran (DBF) was regarded as a model dioxin compound, and V2O5/AC was used as a catalyst to investigate the impact of SO2 on degradation activity and the degradation path of DBF. Various characterization results showed that SO2 could promote the transformation of DBF to intermediates through a reaction with lattice oxygen and lower the apparent activated energy of DBF catalytic oxidation on V2O5/AC catalysts. The density functional theory (DFT) calculations confirmed that SO2 improved the oxidation ability of lattice oxygen on V2O5/AC. The ethyl hydrogen fumarate intermediate decreased and the small-molecule byproducts increased, providing further evidence that SO2 accelerates the degradation of DBF and its intermediates. However, the formation of VOSO4 would inevitably deteriorate the adsorption and oxidation abilities of V2O5/AC. A model is pioneered to describe the relationship between SO2 promotion and VOSO4 inhibition on DBF catalytic oxidation on a V2O5/AC catalyst. This study is expected to provide theoretical guidance for the collaborative abatement of multi-pollutants in flue gas.

Insight into the roles of microenvironment and active site on the mechanism regulation in metal-free persulfate activation process coupling with an electric field.

The regulation of the persulfate activation mechanism is highly desirable and meaningful for the treatment of different wastewaters. The role of active sites for mechanism regulation in carbon-driven persulfate activation is still ambiguous due to the complex and easily neglected microenvironment (concentration distributions of organics and oxidants) nearby carbon catalyst. This work aims to reveal the critical roles of active site and microenvironment on the activation mechanism through N-doped modification and application of an electric field (AC/PS/EC). Several N-doped activated carbon catalysts were prepared by activating for different times to adjust the surface active center and adsorption selectivity under an electric field. The contribution ratio of radical pathway and non-radical pathway for organic elimination significantly varied with the concentration distribution of organics and oxidants nearby the microelectrodes. The increased electro-adsorption of persulfate anion was found to be the primary promoting factor for the radical pathway for organic oxidation, resulting in a synergistic increase in degradation rate in the AC/PS/EC system. The quantitative structure-activity relationships analysis also revealed that the electro-adsorption selectivity was dominated by the surface graphitic N and pore structure of catalyst. This study sheds new light on the oxidative pathway regulation to deal with complex wastewater in a flexible and efficient manner.

Insight into the Transformation Behaviors of Dioxins from Sintering Flue Gas in the Cyclic Thermal Regeneration by the V2O5/AC Catalyst-sorbent.

Dioxins in the sintering flue gas are usually removed through integrated elimination technologies by carbonaceous catalysts. However, the regeneration of the used catalyst is poorly investigated, leading to the risk of leakage of dioxins. Herein, the influences of cyclic regenerations on the dioxin removal performance of a catalyst (V2O5/AC) were investigated systematically with dibenzofuran (DBF) as a model pollutant. It was demonstrated that the adsorption capacity and oxidation activity of catalysts significantly declined after several regeneration cycles due to the decreasing external specific surface area and V5+, respectively. Compared with 79.12% DBF directly emitted from a regenerator during N2 regeneration, the emission of DBF was only 29.93% with the modification of the regeneration process through O2 addition and temperature adjustment. The possible regenerated products were also analyzed to disclose the transformation behaviors of DBF. The regeneration mechanisms of DBF followed the transformation pathway of dibenzofuranol, benzofuran, anhydride species, and ultimately to CO2 and H2O. Moreover, the accumulated heavy aromatics on the surface could be decomposed by introducing O2. This research provides a comprehensive understanding of dioxin transformation behavior and a theoretical basis for efficient control of dioxin removal in the whole integrated removal technologies.

Covalent organic frameworks-derived hierarchically porous N-doped carbon for 2,4-dichlorophenol degradation by activated persulfate: The dual role of graphitic N.

A series of hierarchically porous carbon catalysts with high N content and large surface area were prepared via self-templated carbonization of covalent organic frameworks (COFs). The catalyst was used to activate persulfate (PS) for degrading 2,4-dichlorophenol (2,4-DCP). Experimental results demonstrated that the prepared catalyst treated at 700 °C (PNC-700) showed both strong adsorption ability and enhanced PS activity for 2,4-DCP degradation. A variety of characterization techniques were used to investigate the properties of prepared catalysts. We found that the graphitic N functional groups acted as both activity sites and electron transfer access. The activity of the catalyst was also closely related to the hierarchical pore structure and good electrical conductivity. The influencing factors of PNC-700/PS system in 2,4-DCP degradation were discussed. In addition, PNC-700 displayed excellent recyclability. The activation process especially non-radical pathway was promoted by increasing graphitic N contents. The possible reaction mechanism and degradation pathways were also proposed.

Enhanced organics degradation by three-dimensional (3D) electrochemical activation of persulfate using sulfur-doped carbon particle electrode: The role of thiophene sulfur functional group and specific capacitance.

For further enhancing the electrochemical oxidation performance, sulfur-doped carbon particle electrode was employed in the three-dimensional (3D) electro-assisted activation of persulfate process (ACS/PS/EC). Herein, an in situ S-doped activated carbon (ACS) was prepared and applied as the particle electrode as well as catalyst in ACS/PS/EC system. Several carbon particle electrodes with different annealing temperature were prepared and characterized via EA, BET, XPS and Raman spectra. Cyclic voltammetry (CV) was perform to obtain the specific capacitance and investigate the interfacial electron transfer of ACS particle. The results of comparative experiments showed significant synergy between electric and catalytic activations of PS. Especially, the as-prepared sample treated at 850 °C (ACS-850) exhibited an outstanding catalytic performance, and the phenol degradation rate was greatly improved by nearly 100% with the application of electric field. By comparing of several carbon particle electrodes with different functional groups and specific capacitances, it is revealed that thiophene sulfur functional group is the mainly active site for both electric and catalytic activation of PS, and the specific capacitance acts as assistant factor. Quenching experiments proved that the 3D electro-assisted activation of PS proceeded through both radical and non-radical pathway. Possible mechanism for ACS/PS/EC electrochemical process was proposed.

Degradation of methyl orange by ozone in the presence of ferrous and persulfate ions in a rotating packed bed.

This work investigated the degradation of methyl orange by ozone in the presence of ferrous and persulfate ions (O3/Fe(2+)/S2O8(2-)) in a rotating packed bed. The effects of various operating parameters such as initial pH, rotational speed, gas-liquid ratio, ozone inlet concentration and reaction temperature on the degradation rate of methyl orange were studied with an aim to optimize the operation conditions. Results reveal that the degradation rate increased with an increase in rotational speed, gas-liquid ratio and ozone inlet concentration, and reached a maximum at 25 °C and initial pH 4. Contrast experiments involving ozone and ferrous ions (O3/Fe(2+)) were also carried out, and the results show approximately 10% higher degradation rate and COD removal in the O3/Fe(2+)/S2O8(2-) process than in the O3/Fe(2+) process. Additionally, the intermediates of the degradation process were analyzed to ascertain the degradation products.

Treatment of amoxicillin by O3/Fenton process in a rotating packed bed.

In this study, simulated amoxicillin wastewater was treated by the O3/Fenton process in a rotating packed bed (RPB) and the results were compared with the Fenton process and the O3 followed by Fenton (O3 + Fenton) process. The chemical oxygen demand (COD) removal rate and the ratio of 5-day biological oxygen demand to chemical oxygen demand (BOD5/COD) in the O3/Fenton process were approximately 17% and 26%, respectively, higher than those in the O3 + Fenton process with an initial pH of 3. The COD removal rate of the amoxicillin solution reached maximum at the Fe(II) concentration of 0.6 mM, temperature of 25 °C, rotation speed of 800 rpm and initial pH of 3. The BOD5/COD of the amoxicillin solution increased from 0 to 0.38 after the solution was treated by the O3/Fenton process. Analysis of the intermediates indicated that the pathway of amoxicillin degradation in the O3/Fenton process was similar to that in the O3 + Fenton process. Contrast experiment results showed that amoxicillin degradation was significantly intensified in the RPB.

Ozonation of azo dye Acid Red 14 in a microporous tube-in-tube microchannel reactor: decolorization and mechanism.

The ozonation of synthetic wastewater containing azo dye Acid Red 14 (AR 14) was investigated in a high-throughput microporous tube-in-tube microchannel reactor. The effects of design and operating parameters such as micropore size, annular channel width, liquid volumetric flow rate, ozone-containing gas volumetric flow rate, initial pH of the solution and initial AR 14 concentration on decolorization efficiency and ozone utilization efficiency were studied with the aim to optimize the operation conditions. An increase of the ozone-containing gas or liquid flow rate could greatly intensify the gas-liquid mass transfer. Reducing the micropore size and the annular channel width led to a higher mass transfer rate and was beneficial to decolorization. Decolorization efficiency increased with an increasing ozone-containing gas volumetric flow rate, as well as a decreasing liquid volumetric flow rate and initial AR 14 concentration. The optimum initial pH for AR 14 ozonation was determined as 9.0. The degradation kinetics was observed to be a pseudo-first-order reaction with respect to AR 14 concentration. The difference between the decolorization and COD removal efficiency indicated that many intermediates existed in AR 14 ozonation. The formation of six organic intermediates during ozonation was detected by GC/MS, while the concentration of nitrate and sulfate ions was determined by ion chromatography. The possible degradation mechanism of AR 14 in aqueous solution was proposed.