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Heat-Assisted Visible Light Catalytic PMS for Diclofenac Degradation: Mn-Doped g-C.sub.3N.sub.4 Catalysts and Synergistic Catalytic Mechanism
Different manganese salt precursor-doped g-C.sub.3N.sub.4 catalysts prepared by the mixed calcination method were applied in the heat-assisted visible light catalytic peroxymonosulfate (PMS) activation (Heat/Vis/PMS) system for the degradation of diclofenac (DCF). Under this Heat/Vis/PMS system, the CN-Mn-S catalyst using MnSO.sub.4 as the manganese salt precursor showed the optimal DCF degradation efficiency (96.9%) with the fastest reaction rate (0.1607 min.sup.-1). Besides, with the advantages of large specific surface area, high Mn.sub.3O.sub.4 generation, and good visible light absorption performance, CN-Mn-S catalyst also maintained excellent catalytic activity after five cycles. Electron paramagnetic resonance (EPR) analysis revealed that the generation of active species with relatively high contribution to DCF degradation, including generation of superoxide anion (O.sub.2·.sup.-) and singlet oxygen (.sup.1O.sub.2), were significantly increased in the CN-Mn-S/Heat/Vis/PMS system. Meanwhile, combined with the analysis of influence factor experiments and the DCF degradation characteristics, the CN-Mn-S/Heat/Vis/PMS system was able to maintain excellent DCF degradation ability in complex environments. This work provides a new idea for the application of PMS in real environment.
Journal Article
3D-Graphite Felt Self-loaded Rich Co.sub.3O.sub.4 Nanoparticle Electrodes for Chlorine Evolution Reaction at Low Concentration Chloride Ion
To investigate a highly active catalyst for CER and explore low concentrations of Cl.sup.- electrocatalytic product Cl.sub.2, Co.sub.3O.sub.4/GF catalysts were constructed by a methanesulfonic acid system plating and calcination process. SEM shows Co.sub.3O.sub.4/GF-0.1 has a uniform distribution of nanoparticles. TEM, XRD, and XPS results confirmed the formation of Co.sub.3O.sub.4. The catalytic activity in high concentrations of Cl.sup.- and low concentrations of Cl.sup.- are discussed. LSV suggests Co.sub.3O.sub.4/GF-0.1 with an initial potential of 1.06 V, The overpotential at a current density of 10 mA cm.sup.-2 is 232 m V, Tafel slope 109.26 mV dec.sup.-1, the CER reaction order is 0.54 at 1, 2 and 3 M NaCl, and 0.18 at 4, 5 and 6 M NaCl, too high concentration of Cl.sup.- slow down control of speed. In low concentration solution, the CER reaction order is 0.99, which can achieve the degradation rate of 90.8% in 50 ppm ammonia nitrogen. The apparent constant and the concentration of Cl.sup.- conform to the equation K = 1.44 x 10.sup.-3 C.sub.0.sup.0.95. From low concentration to high concentration, energy consumption decreased, and Faraday efficiency increased. Electrode with j.sub.ECSA = 0.52 mA cm.sup.-2, 3D structure GF has a large specific active area that promotes the diffusion of Cl.sup.-. This work provides analysis methods and ideas for the preparation of the high activity and stability CER catalyst at low Cl.sup.- concentrations in the actual water body.
Journal Article
Performance of Mn-Ce-Fe/FA Catalysts on Selective Catalytic Reduction of NOsub.X with CO under Different Atmospheres
Gas turbines produce a large amount of NO[sub.x] and CO due to high temperatures and insufficient combustion. Through the selective catalytic reduction of NO with CO (CO-SCR) in a gas turbine, the activities of the Mn-Fe-Ce/FA catalyst using fly ash (FA) as a carrier under different atmospheres were studied. The catalysts prepared by calcining different active materials under different atmospheres were used to analyze their denitrification abilities and resistance to water vapor. The denitrification performance of the catalyst prepared under reducing atmosphere is about 30 percent higher than that of the catalyst prepared under air atmosphere, and the decarburization performance is about 40 percent higher. In the presence of oxygen, the denitrification rate and decarburization rate of the 1:1 ratio of the Mn-Ce catalyst reach 67.16% and 59.57%, respectively. In an oxygen-containing atmosphere, the catalyst prepared by replacing Ce with Fe shows better denitrification and decarburization performances, which are 78.56% and 78.39%, respectively. When the flue gas space velocity is 4000 h[sup.−1] and the carbon-nitrogen ratio is 1.6, the catalyst shows better performance. After the water vapor is introduced, the denitrification and decarbonization rates of the catalyst decrease by about 10% and 9%, respectively. After ceasing water vapor, it rebounds by about 8%, and the activity could not be fully restored. However, the catalyst still shows strong water resistance in general.
Journal Article
Poisoning Effects of Chlorine on V.sub.2O.sub.5-WO.sub.3/TiO.sub.2 Catalysts for Selective Catalytic Reduction of NO.sub.x by NH.sub.3
Chlorine species, widely presented in industrial flue gas such as the waste incineration plants, can poison the catalysts and affect the selective catalytic reduction (SCR) performance. In this work, effects of Cl on the SCR performance of V.sub.2O.sub.5-WO.sub.3/TiO.sub.2 (VW/Ti) catalysts were investigated by NH.sub.4Cl deposition. The results showed that the NO.sub.x conversion efficiency at low reaction temperature (< 300 °C) decreased with the loading of NH.sub.4Cl after calcination. It was found that instead of causing the chlorination of VW/Ti catalyst the NH.sub.4Cl decomposed into volatile Cl species due to the weak V-Cl bonding. Such decomposition reduced significantly the surface non-lattice oxygen species to inhibit NO adsorption and activation, but hardly affected the redox ability and acidity of VW/Ti catalyst. Time-resolved in situ DRIFTs results indicated that NH.sub.3 activation and the SCR process predominated by Eley-Rideal mechanism were not influenced with NH.sub.4Cl impregnation, while the SCR at low temperature following a Langmuir-Hinshelwood path was limited by the decreased and weaker binding sites for NO activation.
Journal Article
Are Rh Catalysts a Suitable Choice for Bio-Oil Reforming? The Case of a Commercial Rh Catalyst in the Combined Hsub.2O and COsub.2 Reforming of Bio-Oil
Bio-oil combined steam/dry reforming (CSDR) with H[sub.2]O and CO[sub.2] as reactants is an attractive route for the joint valorization of CO[sub.2] and biomass towards the sustainable production of syngas (H[sub.2] + CO). The technological development of the process requires the use of an active and stable catalyst, but also special attention should be paid to its regeneration capacity due to the unavoidable and quite rapid catalyst deactivation in the reforming of bio-oil. In this work, a commercial Rh/ZDC (zirconium-doped ceria) catalyst was tested for reaction–regeneration cycles in the bio-oil CSDR in a fluidized bed reactor, which is beneficial for attaining an isothermal operation and, moreover, minimizes catalyst deactivation by coke deposition compared to a fixed-bed reactor. The fresh, spent, and regenerated catalysts were characterized using either N[sub.2] physisorption, H[sub.2]-TPR, TPO, SEM, TEM, or XRD. The Rh/ZDC catalyst is initially highly active for the syngas production (yield of 77% and H[sub.2]/CO ratio of 1.2) and for valorizing CO[sub.2] (conversion of 22%) at 700 °C, with space time of 0.125 g[sub.catalyst] h (g[sub.oxygenates])[sup.−1] and CO[sub.2]/H[sub.2]O/C ratio of 0.6/0.5/1. The catalyst activity evolves in different periods that evidence a selective deactivation of the catalyst for the reforming reactions of the different compounds, with the CH[sub.4] reforming reactions (with both steam and CO[sub.2]) being more rapidly affected by catalyst deactivation than the reforming of hydrocarbons or oxygenates. After regeneration, the catalyst’s textural properties are not completely restored and there is a change in the Rh–support interaction that irreversibly deactivates the catalyst for the CH[sub.4] reforming reactions (both SR and DR). As a result, the coke formed over the regenerated catalyst is different from that over the fresh catalyst, being an amorphous mass (of probably turbostractic nature) that encapsulates the catalyst and causes rapid deactivation.
Journal Article
Supported Inverse MnOsub.x/Pt Catalysts Facilitate Reverse Water Gas Shift Reaction
Catalytic conversion of CO[sub.2] to CO via the reverse water gas shift (RWGS) reaction has been identified as a promising approach for CO[sub.2] utilization and mitigation of CO[sub.2] emissions. Bare Pt shows low activity for the RWGS reaction due to its low oxophilicity, with few research works having concentrated on the inverse metal oxide/Pt catalyst for the RWGS reaction. In this work, MnO[sub.x] was deposited on the Pt surface over a SiO[sub.2] support to prepare the MnO[sub.x]/Pt inverse catalyst via a co-impregnation method. Addition of 0.5 wt% Mn to 1 wt% Pt/SiO[sub.2] improved the intrinsic reaction rate and turnover frequency at 400 °C by two and twelve times, respectively. Characterizations indicate that MnO[sub.x] partially encapsulates the surface of the Pt particles and the coverage increases with increasing Mn content, which resembles the concept of strong metal–support interaction (SMSI). Although the surface accessible Pt sites are reduced, new MnO[sub.x]/Pt interfacial perimeter sites are created, which provide both hydrogenation and C-O activation functionalities synergistically due to the close proximity between Pt and MnO[sub.x] at the interface, and therefore improve the activity. Moreover, the stability is also significantly improved due to the coverage of Pt by MnO[sub.x]. This work demonstrates a simple method to tune the oxide/metal interfacial sites of inverse Pt-based catalyst for the RWGS reaction.
Journal Article
The Effect of SO.sub.2 and Ca Co-pretreatment on the Catalytic Activity of Mn-Ce/TiO.sub.2 Catalysts for Selective Catalytic Reduction of NO with NH.sub.3
Mn-Ce/TiO.sub.2 catalysts were co-pretreated with SO.sub.2 and Ca and applied for the selective catalytic reduction (SCR) of NO with ammonia. The effect of co-pretreatment of SO.sub.2 and Ca on the physicochemical properties of catalysts was investigated by BET, XRD, XPS, NH.sub.3-TPD, H.sub.2-TPR, and UV-Vis techniques. The results show the co-pretreatment of SO.sub.2 and Ca greatly influences the physicochemical properties of catalysts such as texture characteristics, surface acidity and redox ability, amounts of active species and surface OH group, and therefore affects the catalytic activity of catalysts. The Mn-Ce-Ti(S-OH) catalyst co-pretreated with SO.sub.2 and Ca(OH).sub.2 exhibits better catalytic activity than Mn-Ce-Ti(S-Cl) catalyst co-pretreated with SO.sub.2 and CaCl.sub.2. The Mn-Ce-Ti(S-OH) catalyst possesses larger specific surface area, higher concentrations of surface active species and surface chemisorbed oxygen, better surface acidity and redox ability, which may contribute to the accelerated catalytic activity.
Journal Article