PtNi alloy nanoparticles supported on carbon (XC-72) are synthesized via a one-pot synthetic approach. This synthesized bimetallic composite offers several advantages, such as reduction of precious Pt along with an increase in activity due to the modified electronic structure. The prepared PtNi/C catalysts were employed as catalysts for NO removal both in a fixed-bed reactor and in a newly designed gas diffusion reactor. The performances of all prepared PtNi/C catalysts were higher than Pt/C at the same conditions and maintained a stable NO removal at a wide temperature window (100–300 °C), especially for Pt65Ni35 (more than 95% from 120 to 300 °C). This is attractive for low temperature SCR technology. According to XPS analysis, the surface layer phase was comprised of Pt contents with Ni being localized beneath the successive layers until Ni content increased to 67% mole ratio. The surface presence of Ni significantly affects the Pt electronic structure and raises the mass specific activity of Pt. Meanwhile, PtNi/C catalysts were introduced in a new gas diffusion reactor to remove NO under quantitatively less catalysts (30 mg), high NO concentration (1000 ppm), and at a high flow rate (resulting in a very short residence time of 0.09 s) condition. NO removal reaches almost 100% below 95 °C for all the PtNi catalysts and among all Pt65Ni35 exhibited the best performance. In addition, the influence of SO2 on the performance of Pt65Ni35 was also investigated, and the catalysts exposed a good antipoisonous property. The excellent performance of PtNi catalysts and a gas diffusion reactor are strongly recommended for their utilization as highly active and economical technology for NO removal.Keywords: Gas diffusion; H2−SCR; NOx; PtNi;

Developing more efficient and stable oxygen evolution reaction (OER) catalysts is critical for future energy conversion and storage technologies. We demonstrate that inducing a lattice strain in IrO2 crystal structure due to interface lattice mismatch enables an enhancement of the OER catalytic activity. The lattice strain is obtained by the direct growth of IrO2 nanoparticles on a specially exposed surface of α-MnO2 nanorods via a simple two-step hydrothermal synthesis. Interestingly, the prepared hydride OER activity increases with a lower IrO2 grown mass, which offers an opportunity to reduce the usage of precious iridium and ultimately obtains a specific mass activity of 3.7 times than that of IrO2 prepared under the same conditions and exhibits equivalent stability. The lattice mismatch in the underlying interface induces the formation of lattice strain in IrO2 rather than the charge transfer between the materials. The lattice strain changes are in good agreement with the order of the OER activity. Our experimental results indicate that using the special exposed surface substrates or tuning the supporting morphology structure can manipulate the catalyst materials lattice strain for the design of more efficient OER catalysts.Keywords: interface mismatch; IrO2; lattice strain; OER; α-MnO2;

In this paper, Pt supports on carbon black powder (Vulcan XC-72) were synthesized via a hydrothermal method for selective catalytic reduction (SCR) of NO with H2 in the presence of 2 vol% O2 over a wide temperature of 20–300 °C. The results showed that the 3 and 5 wt% Pt/C catalysts resulted in high NO conversion (>90 %) over a temperature range of 120 to 300 °C, and the maximum NO conversion of 98.6 % was achieved over 5 wt% Pt/C at 120 °C. Meanwhile, the influence of SO2 and H2O on the catalyst performance of 3 wt% Pt/C was investigated. The catalysts exhibited good SO2 poisoning resistance when the SO2 concentration was lower than 260 ppm. Moreover, a positive effect on NO conversion was detected with the addition of 3 and 5 vol% H2O in the feed gas stream.

A novel cryptomelane-Ir (cry-Ir) electrode is prepared for Ir to enter into the cryptomelane (named as cry-Mn) structure and used for aspirin degradation. This catalyst can efficiently reduce the Ir usage from 85 to 34%. Also, the onset potential of cry-Ir is about 1.40 V and the over potential is about 0.34 V at 10 mA cm−2, indicating that cry-Ir has an excellent oxygen evolution reaction (OER) activity to produce oxidizing species and can decrease electrolytic voltage during the electro-oxidation process. So, the electrical efficiency per log order (EE/O) for cry-Ir electrode is only 5% of PbO2 electrode, which is the best electrode for organic degradation. Also, cry-Ir has large tunnel size which favors insertion of aspirin molecule into cry-Ir structure and enhances the contact between reactive intermediates and the contaminant. Using cry-Ir as anode, 100% aspirin removal and 55% chemical oxygen demand (COD) removal could be obtained at 4 V. We also compare cry-Ir electrode with IrO2 and find that IrO2 anode can only eliminate 20% aspirin under the same condition. As a result, cry-Ir is a promising anode material for organic pollutant degradation.

Limited Pd-doped Mn-based spinel catalysts were prepared for selective catalytic reduction by H2 at low temperature. NiMn1.95Pd0.05O4 catalyst displayed maximum NO conversion of 96% at 150 °C, representing high efficiency compared with non-palladium-doped manganate spinels. The order of activity was: NiMn1.95Pd0.05O4 > CuMn1.95Pd0.05O4 > CoMn1.95Pd0.05O4, consistent with their Brunauer–Emmett–Teller (BET) surface area, indicating that large surface area favored the reaction. X-ray diffraction (XRD) data proved that the catalysts had perfect spinel structure. When SO2 was added to the feed stream, the conversion of NO decreased due to competitive adsorption with NO and formation of sulfite and sulfate on the catalyst surface. The effect of 3 and 5% H2O was also tested, with the original conversion level of 95% being retained and the water vapor removed from the stream, representing excellent water tolerance.

•95% of NO conversion was achieved over Co-AlPd catalyst at 230–250 °C.•Both of the pure and Pd-doped aluminate spinels showed the same orders in activity.•Positive influence of the NO conversion was achieved in the presence of 5% H2O.•The prepared catalysts contained excellent SO2 tolerance.The performance of pure and Pd-doped aluminate spinel catalysts (i.e., MAl2O4 and MAl1.95Pd0.05O4, where M = Cu, Co, Zn) for the selective catalytic reduction of NO by H2 (H2-SCR) were investigated in this paper. The catalytic performance over MAl2O4 is poor but can be improved significantly by incorporating Pd into the lattice, resulting in NO conversion over Co-AlPd, Zn-AlPd and Cu-AlPd catalysts of approximately 95%, 90.5% and 84%, respectively, in the presence of 2% O2 at a low temperature range of 100–350 °C. Both the pure and Pd-doped aluminate spinel catalysts showed the same sequences with respect to activity: Co-Al > Zn-Al > Cu-Al and Co-AlPd > Zn-AlPd > Cu-AlPd, indicating that the selection of divalent metal M is of essential importance in designing spinel catalysts and in modifying their SCR performance. Co-AlPd catalyst showed stable activity in the presence of 3% and 5% H2O at 250 °C, whereas the SCR reaction was promoted and a slight positive influence of the NO conversion was observed with a further increase of the H2O concentration to 5%. The presence of 100 ppm SO2 in the feed resulted in almost a 23% NO reduction at 250 °C for the Co-AlPd catalyst, whereas only a 1.2% decrease of NO conversion was observed with further increase in the SO2 concentration to 150 ppm, and the NO conversion recovered rapidly to approximately 82% after removing the SO2 from the feed stream.Download high-res image (197KB)Download full-size image

•A novel diffusion electrochemical reactor was proposed to remove Hg0.•The reaction mechanism of Hg0 removal was investigated.•Hydrogen peroxide and hydroxyl radicals play a dominant role for Hg0 removal.A diffusion electrochemical reactor was proposed to remove elemental mercury (Hg0) from coal-fired flue gas. The experiments were carried out in an undivided column reactor with a self-made gas diffusion electrode (GDE) as cathode and Ti/IrO2 as anode. Hg0 was oxidized when the simulated gas passed through GDE. It turned out that the removal of Hg0 in electrochemical process was dominated by electro-generated H2O2 and free radicals on GDE interface or in the electrolyte. Under 70 °C, Hg0 removal efficiency exceeded 90% after 40 min electrolysis. The effects of operation parameters were investigated and the results demonstrated that voltage, gas flow rate, and initial concentration of Hg0 had significant influences on Hg0 removal, especially the reaction temperature, electrolyte concentration and pH. H2O2 and HO in the electrolyte were measured by UV–vis spectrophotometer and electron spin resonance (ESR), respectively. The above results show that electrochemical technique is a promising method for emission control of Hg0 from coal-fired flue gas.Download full-size image

•Kx≈0.25IrO2 (h-Ir) is a novel catalyst to degrade sulpiride.•First to assemble catalyst to three dimensional structure Ti foam.•h-Ir can effectively reduce the overall energy consumption.The electrochemical oxidation processes have been proven as an efficient and environment-friendly techniques to degrade the organic contaminants. However, higher energy consumption and lower efficiency restrict the commercial applications on large scale. The conventional viewpoint to design anodes for the electrochemical degradation applications is to avoid the OER occurrence. However, the OER not only plays a positive role in preventing anodic fouling, but also produces various activated oxygen species (O*, OH* and OOH*) to benefit oxidation of organic pollutants. Here, we demonstrate that a novel catalyst Kx≈0.25IrO2 has a unique tunnel structure and d bands, when fixed on Ti foam to form a three dimensional (3D) architecture anode, can efficiently degrade the sulpiride both in acidic and neutral solution. It can achieve 61% mineralization in acidic environment, which is five times higher than that of IrO2 under the same condition and two times higher than that of performed Fenton degradation. This 3D architecture not only provides a large surface area but also escalates the mass transfer, which is a crucial factor for the SP degradation. In short, we demonstrate that the tunnel structure catalyst along with high OER activity not only provides an attractive degradation performance, but can reduce the cell potential to decrease the energy consumption.Download high-res image (124KB)Download full-size image

The oxygen evolution reaction (OER) is a critical half reaction for energy storage techniques and is regarded as a major challenge due to its sluggish kinetics and complex reaction mechanism. The traditional OER catalysts, such as IrO2, RuO2 and their binary or ternary oxides, have finite large-scale commercial applications due to their significant cost and rareness. Here, we hydrothermally synthesized cry-Ir by doping Ir into non-OER active cryptomelane-type manganese oxide to significantly reduce the Ir mass ratio by 60.3% from 85.7% in IrO2 to 34% in the developed catalyst, along with higher OER performance with a lower onset potential and 10 times higher specific mass activity. The special tunnel structure of cryptomelane plays an important role in promoting its OER activity through facilitating water molecular insertion into the tunnel. We combined Raman, XPS and TEM mapping to confirm that no IrO2 composite is present on the cry-Ir surface. The XPS and XAS spectra indicate substitution of Ir4+ on the Mn3+ site and the presence of more 5d states in the Ir site compared to IrO2. The differences in VBS spectra between cry-Ir, IrO2 and cry-Mn indicate that the electronic structure of Ir sites is modified when Ir substitutes Mn3+ sites. Thus, this special tunnel structure and modified Ir electronic structure in cry-Ir are responsible for the outstanding OER performance. Our studies provide an approach for designing effective Ir-based OER catalysts whilst significantly reducing the consumption of precious elements.

Oxygen evolution reaction (OER) catalysts with high activity are of particular importance for renewable energy production and storage. Here, we prepare Kx≈0.25IrO2 catalyst that exhibits an excellent OER activity compared to IrO2, which is univerally acknoweledged as a state-of-the-art OER catalyst. The prepared catalyst reflects a small overpotential 0.35 V at a current density of 10 mA cm–2 and a lower Tafel slope (65 mV dec–1) compared to that for IrO2 (74 mV dec–1). The performed X-ray photoelectron spectroscopy (XPS) and X-ray adsorption (XAS) experiments indicate that the Ir-site of Kx≈0.25IrO2 has a lower valence and more Ir-5d occupied states, suggesting more electrons on the Ir site. The extra electrons located on the Ir site and distorted IrO6 octahedral symmetry have a significant effect on the 5d orbital energy distribution which is verified by our DOS calculation. The performed DFT calculations state that the Kx≈0.25IrO2 essentially obtains good OER performance because it has a lower theoretical overpotential (0.50 V) compared to IrO2 (0.61 V).Keywords: DFT; electronic structure; hollandite iridate; hydrothermal; OER

H2 selective catalytic reduction (H2-SCR) has been proposed as a promising technology for controlling NOx emission because hydrogen is clean and does not emit greenhouse gases. We demonstrate that Pt doped into a nickel ferrite spinel structure can afford a high catalytic activity of H2-SCR. A superior NO conversion of 96% can be achieved by employing a novel NiFe1.95Pt0.05O4 spinel-type catalyst at 60 °C. This novel catalyst is different from traditional H2-SCR catalysts, which focus on the role of metallic Pt species and neglect the effect of oxidized Pt states in the reduction of NO. The obtained Raman and XPS spectra indicate that Pt in the spinel lattice has different valence states with Pt2+ occupying the tetrahedral sites and Pt4+ residing in the octahedral ones. These oxidation states of Pt enhance the back-donation process, and the lack of filling electrons of the 5d band causes Pt to more readily hybridize with the 5σ orbital of the NO molecule, especially for octahedral Pt4+, which enhances the NO chemisorption on the Pt sites. We also performed DFT calculations to confirm the enhancement of adsorption of NO onto Pt sites when doped into the Ni–Fe spinel structure. The prepared Pt/Ni–Fe catalysts indicate that increasing the dispersity of Pt on the surfaces of the individual Ni–Fe spinel-type catalysts can efficiently promote the H2-SCR activity. Our demonstration provides new insight into designing advanced catalysts for H2-SCR.Keywords: H2-SCR; nickel ferrite spinel; NO adsorption; Pt

•A model of an electro-reactor for recycling and resource recovery was developed.•The model accounts for geometrical factors, bubble formation, and mass transport.•The analytical solutions were agreed well with the numerical solutions.•The developed model is helpful to gain a deeper understanding of the process.A mathematical model of a three-compartment electro-reactor process with ion-exchange membranes for recycling and resource recovery of desulfurization residuals was developed. This model describes the electrochemical separation process in the bulk solution and the diffusion boundary layer close to the membrane surfaces with a multiphysics-based approach. This approach considered the following mechanisms: diffusion and migration in different control volumes, the effect of bubbles, the effect of the geometry of the reactor, and the electrochemical reactions of the gases. The analytical solution to the developed model was obtained using a Laplace transformation, and the numerical solution was solved in Wolfram Mathematica and COMSOL Multiphysics. All analytical solutions exhibit a good agreement with the numerical solutions. The analysis of the model revealed that the following parameters may have a positive effect on the performance of the electro-reactor: (1) a high concentration gradient across the membrane enhances mass transport; (2) the current density is the key controlling parameter for both mass transport and bubble formation; (3) a small gap in the cell spacer may improve the performance of the reactor; (4) appropriate effective areas of the membrane for mass transfer guarantees high performance.

A heterojunction thin film consisting of n-type titanium dioxide (TiO2) and p-type cuprous oxide (Cu2O) was fabricated on an FTO conducting glass. The TiO2 films were grown on the FTO glass by sol–gel and spray pyrolysis methods, and Cu2O was deposited on it via the hydrothermal method. The morphology, crystalline structure, and optical absorption characteristics were studied by scanning electron microscopy, X-ray diffraction, and ultraviolet–visible diffuse reflectance spectrum, respectively. The results show that the surface of the Cu2O/TiO2 film was composed of net and large grains, which contributed to a large specific surface area. The crystal phase of the TiO2 in the Cu2O/TiO2 film remained anatase. The crystal phase of the Cu2O could not be detected as it is found in traces. The Cu2O/TiO2 film had a stronger optical absorption ability than the pure TiO2 film. To investigate catalytic activity, a photocatalytic degradation experiment of the Cu2O/TiO2 film was performed in a homemade thin-layer micro-reactor. The photocatalytic degradation of methylene blue increased with increasing amounts of deposited Cu2O until a maximum limit was reached. The photocatalytic activity might have declined with an increase in Cu2O content. The metallic oxide has the potential to screen other photocatalysts from the UV source.

The oxygen evolution reaction (OER) has been regarded as a key half reaction for energy conversion technologies and requires high energy to create OO bonds. Transition metal oxides (TMOs) seem to be a promising and appealing solution to the challenge because of the diversity of their d-orbital states. We chose IrO2 as a model because it is universally accepted as a current state-of-the-art OER catalyst. In this study, copper-doped IrO2, particularly Cu0.3Ir0.7Oδ, is shown to significantly improve the OER activity in acidic, neutral and basic solutions compared to un-doped IrO2. The substituted amount of Cu in IrO2 has a limit described by the Cu0.3Ir0.7Oδ composition. We determined that the performance of Cu0.3Ir0.7Oδ is due primarily to an increase in the Jahn–Teller effect in the CuO6 octahedra, and partially to oxygen defects in the lattice induced by the IrO6 octahedral geometric structure distortions, which enhance the lift degeneracy of the t2g and eg orbitals, making the dz2 orbital partially occupied. This phenomenon efficiently reduces the difference between ΔG2 and ΔG3 in the free energy from the density functional theoretical (DFT) calculations and can yield a lower theoretical overpotential comparable to that of IrO2. The proposed method of doping with foreign elements to tune the electron occupation between the t2g and eg orbital states of Ir creates an opportunity for designing effective OER catalysts using the TMO groups.

The economical production of hydrogen and the circulating regeneration of the sulfur dioxide adsorbent from the residuals of flue gas desulfurization were achieved in the electromembrane reactor designed in this work. The theoretical and practical considerations and a discussion of the design and operation of such a reactor are described herein. The average current efficiency of hydrogen production can reach up to 92.32% under the selected optimal operating conditions, with an average hydrogen conversion efficiency of 38.90%, which is close to the theoretical efficiency of 41.43%. The cost of hydrogen production is 8.08 $/(kg of H2) or 2.59 $/(kg of H2) using off-peak electricity, which are both lower than the hydrogen selling price of a small neighborhood-sized market. In addition, according to empirical calculations, regenerating the consumed adsorbent after combusting 1 ton of coal containing 1% sulfur and the flue gas desulfurization process will simultaneously produce approximately 5.50 m3 of hydrogen.

The combined concentrator/oxidizer system has been proposed as an effective physical-chemical option and proven to be a viable solution that enables Volatile Organic Carbons (VOCs) emitters to comply with the regulations. In this work, a field scale honeycomb zeolite rotor concentrator combined with a recuperative oxidizer was developed and applied for the treatment of the VOC waste gas. The research shows the following: (1) for the adsorption rotor, zeolite is a more appropriate material than Granular Activated Carbon (GAC). The designing and operation parameters of the concentrator were discussed in detail including the size and the optimal rotation speed of rotor. Also the developed rotor performance’s was evaluated in the field; (2) Direct Fired Thermal Oxidizer (DFTO), Recuperative Oxidizer (RO), Regenerative Thermal Oxidizer (RTO) and Regenerative Catalytic oxidizer (RCO) are the available incinerators and the RO was selected as the oxidizer in this work; (3) The overall performance of the developed rotor/oxidizer was explored in a field scale under varying conditions; (4) The energy saving strategy was fulfilled by reducing heat loss from the oxidizer and recovering heat from the exhaust gas. Data shows that the developed rotor/oxidizer could remove over 95% VOCs with reasonable cost and this could be helpful for similar plants when considering VOC abatement.

Desulfurization residuals (using NaOH sorbent) were regenerated electrochemically, and at the same time sulfur in the flue gas was recovered as H2SO4 and H2 was produced as a clean energy. Since industrialization should always be the final goal to pursue for lab technologies and the evolution of pilot- and full-scale commercial reactors has taken place relatively slowly, this paper is aimed to develop an electroreactor on a sufficiently large scale to evaluate the application potential of the proposed regeneration process. The following key design parameters are discussed: (1) voltage distributions over electrode, membrane, and electrolyte; and (2) scaling up correlation based on lab-scale reactor operation parameters. Thereafter, in the developed reactor, the desulfurization residuals using NaOH sorbent from a semidry flue gas desulfurization (FGD) facility of a power plant in Shandong Province were regenerated and it is significant to note that the electrochemical efficiency of the designed reactor is comparable to that of the chlor-alkali industry, showing that the technology is environmentally friendly and economically feasible. If this technology is to be employed for FGD, the facility could be a profit-generating manufacturing part instead of a currently money-consuming burden for the plants.

Gaseous oxidation in liquid phase (GOLP) process was proposed to degrade high concentration ammonium in water. The innovative concept behind the reactor design is that the monocrystalline silicon chip coated with catalyst could be heated instantaneously by direct current, which will gasify the surrounding ammonium solution and later catalytically convert it to harmless N2. It is found out that Co3O4 instead of Co2O3 is the active catalytic component in the GOLP process and it coats the silicon chip evenly with nut-shell particle. The experimental results reveal that the GOLP process could degrade high concentration NH4+ efficiently, in which when the current was 10 A, the reactor could remove almost 98% NH4+ after 2 h treatment, at the initial concentration 1810 mg L−1. The overall GOLP process for de-nitrification could be presumed to have two steps: (1) the gasification of liquid around catalyst; and (2) catalytic conversion of NH4+ to N2, which is experimentally demonstrated by Ion Chromatography data. Also, the influences of current and pH were investigated to optimize the operating parameters for the GOLP reactor, and the preliminary energy consumption analysis based on lab data was provided for future reference. These results show that the GOLP process will be able to sustain without extra energy input theoretically if the ammonia concentration is higher than 1.48%.

The oxygen evolution reaction (OER) has been regarded as a key half reaction for energy conversion technologies and requires high energy to create OO bonds. Transition metal oxides (TMOs) seem to be a promising and appealing solution to the challenge because of the diversity of their d-orbital states. We chose IrO2 as a model because it is universally accepted as a current state-of-the-art OER catalyst. In this study, copper-doped IrO2, particularly Cu0.3Ir0.7Oδ, is shown to significantly improve the OER activity in acidic, neutral and basic solutions compared to un-doped IrO2. The substituted amount of Cu in IrO2 has a limit described by the Cu0.3Ir0.7Oδ composition. We determined that the performance of Cu0.3Ir0.7Oδ is due primarily to an increase in the Jahn–Teller effect in the CuO6 octahedra, and partially to oxygen defects in the lattice induced by the IrO6 octahedral geometric structure distortions, which enhance the lift degeneracy of the t2g and eg orbitals, making the dz2 orbital partially occupied. This phenomenon efficiently reduces the difference between ΔG2 and ΔG3 in the free energy from the density functional theoretical (DFT) calculations and can yield a lower theoretical overpotential comparable to that of IrO2. The proposed method of doping with foreign elements to tune the electron occupation between the t2g and eg orbital states of Ir creates an opportunity for designing effective OER catalysts using the TMO groups.

The oxygen evolution reaction (OER) is a critical half reaction for energy storage techniques and is regarded as a major challenge due to its sluggish kinetics and complex reaction mechanism. The traditional OER catalysts, such as IrO2, RuO2 and their binary or ternary oxides, have finite large-scale commercial applications due to their significant cost and rareness. Here, we hydrothermally synthesized cry-Ir by doping Ir into non-OER active cryptomelane-type manganese oxide to significantly reduce the Ir mass ratio by 60.3% from 85.7% in IrO2 to 34% in the developed catalyst, along with higher OER performance with a lower onset potential and 10 times higher specific mass activity. The special tunnel structure of cryptomelane plays an important role in promoting its OER activity through facilitating water molecular insertion into the tunnel. We combined Raman, XPS and TEM mapping to confirm that no IrO2 composite is present on the cry-Ir surface. The XPS and XAS spectra indicate substitution of Ir4+ on the Mn3+ site and the presence of more 5d states in the Ir site compared to IrO2. The differences in VBS spectra between cry-Ir, IrO2 and cry-Mn indicate that the electronic structure of Ir sites is modified when Ir substitutes Mn3+ sites. Thus, this special tunnel structure and modified Ir electronic structure in cry-Ir are responsible for the outstanding OER performance. Our studies provide an approach for designing effective Ir-based OER catalysts whilst significantly reducing the consumption of precious elements.