Catalyst Phase Research Articles

Investigation of the promotion effect of metal oxides on the water-gas shift reaction activity over Pt-MOx/CeO2 catalysts for aqueous phase reforming

Aqueous phase reforming (APR) of methanol is a potential pathway for the effective hydrogen production under relatively mild conditions. The Pt/CeO2 and a series of Pt-MOx/CeO2 (M = Fe, Cr, Mg, Mn) catalysts were prepared by sequential impregnation method and their APR reaction performances were studied. The catalyst properties including valence state of the promoters, the amount of oxygen vacancies, the metal distributions, the adsorption properties of CO and the acidity/basicity of catalysts were characterized and analyzed by XPS, XRD, TEM, CO-TPD, NH3-TPD, CO2-TPD, etc. It was found that the addition of MOx weakened the Pt-CeO2 interaction and promoted the generation of Ptδ+ species with lower valence state, which contribute to the C–H bond cleavage and facilitate methanol conversion. The highest hydrogen production (164.78 mmol) and relatively low CO and CH4 selectivities were obtained over the Pt-MgO/CeO2, while the highest CH4 selectivity was obtained over the Pt-CrOx/CeO2 (2.21%). Over the Pt/CeO2 and Pt-MOx/CeO2 (M = Fe, Cr, Mg, Mn) catalysts, CO2/CH4 ratio correlated well with the catalyst basicity, indicating that the basicity promotes the dissociation adsorption of H2O as well as the water-gas shift (WGS) reaction activity and decreases the methanation activity.

Magnetically recoverable Pd-SILP-Fe3O4@SiO2 catalyst for the Suzuki–Miyaura cross-coupling

An efficient method for the synthesis of range of biaryl through Suzuki-Miyaura cross-coupling of a variety of aryl boronic acids with aryl halides employing highly water dispersible, magnetically separable, palladium tagged, magnetic nanoparticle supported, ionic liquid phase catalyst (Pd-SILP-Fe3O4@SiO2) in water under aerobic conditions has been developed. This nanocatalyst exhibited high thermal stability, high catalytic efficiency, high turnover frequencies (TOF), compatibility in aqueous systems, easy magnetic recovery, and reusability up to 6th run. The major advantages of this method are mild reaction conditions, easy set-up, easy workup, low Pd loading (0.00084 mol% of Pd), higher yields, and use of water as a green solvent, which makes it both environmentally and economically appealing.

Pd-SILP-Fe3O4@SiO2: An efficient supported ionic liquid phase catalyst for the Mizoroki-Heck coupling

An efficient method for the Mizoroki-Heck coupling of aryl halides with alkenes employing already reported palladium tagged, magnetic nanoparticle supported, ionic liquid phase catalyst (Pd-SILP-Fe3O4@SiO2) in water under aerobic conditions has been developed. Various di-substituted alkenes were synthesized with excellent yields using a highly water dispersible Pd-SILP-Fe3O4@SiO2 catalyst. This nanocatalyst displayed high thermal stability, compatibility in aqueous systems, high catalytic efficiency, high turnover frequencies (TOF), easy magnetic recovery, and reusability up to 6th run. The main advantages of the protocol are its robustness, mild reaction conditions, easy set-up, easy workup, low Pd loading (0.001 mol% of Pd), higher yields, and use of water as a green solvent, which makes it both environmentally and economically appealing.

In Situ X-ray Diffraction as a Basic Tool to Study Oxide and Metal Oxide Catalysts

X-ray diffraction (XRD) is a standard technique that is widely applied in heterogeneous catalysis to determine phase composition, atomic structure, and size of crystallites. This review is focused on the application of in situ XRD for studying the catalysts during their “lifetime” (under synthesis, activation, operation, and deactivation conditions), limiting the objects of research to oxide and metal oxide catalysts. Also included is a brief overview of modern techniques and instruments and the latest works illustrating different aspects of this technique in catalyst research. The main conclusion is that the field of heterogeneous catalysis research would benefit substantially from the application of in situ XRD for the structural, phase, and morphological characterization of solid catalysts. Even more useful information can be obtained if XRD is combined with other techniques that are more sensitive at length scales different from that of XRD.

In situ infrared, Raman and X-ray spectroscopy for the mechanistic understanding of hydrogen evolution reaction

Hydrogen production by water reduction reactions has received considerable attention because hydrogen is considered a clean-energy carrier, key for a sustainable energy future. Computational methods have been widely used to study the reaction mechanism of the hydrogen evolution reaction (HER), but the calculation results need to be supported by experimental results and direct evidence to confirm the mechanistic insights. In this review, we discuss the fundamental principles of the in situ spectroscopic strategy and a theoretical model for a mechanistic understanding of the HER. In addition, we investigate recent studies by in situ Fourier transform infrared (FTIR), Raman spectroscopy, and X-ray absorption spectroscopy (XAS) and cover new findings that occur at the catalyst–electrolyte interface during HER. These spectroscopic strategies provide practical ways to elucidate catalyst phase, reaction intermediate, catalyst-electrolyte interface, intermediate binding energy, metal valency state, and coordination environment during HER.

Elucidating the active phases of CoOx films on Au(111) in the CO oxidation reaction

Noble metals supported on reducible oxides, like CoOx and TiOx, exhibit superior activity in many chemical reactions, but the origin of the increased activity is not well understood. To answer this question we studied thin films of CoOx supported on an Au(111) single crystal surface as a model for the CO oxidation reaction. We show that three reaction regimes exist in response to chemical and topographic restructuring of the CoOx catalyst as a function of reactant gas phase CO/O2 stoichiometry and temperature. Under oxygen-lean conditions and moderate temperatures (≤150 °C), partially oxidized films (CoOx<1) containing Co0 were found to be efficient catalysts. In contrast, stoichiometric CoO films containing only Co2+ form carbonates in the presence of CO that poison the reaction below 300 °C. Under oxygen-rich conditions a more oxidized catalyst phase (CoOx>1) forms containing Co3+ species that are effective in a wide temperature range. Resonant photoemission spectroscopy (ResPES) revealed the unique role of Co3+ sites in catalyzing the CO oxidation. Density function theory (DFT) calculations provided deeper insights into the pathway and free energy barriers for the reactions on these oxide phases. These findings in this work highlight the versatility of catalysts and their evolution to form different active phases, both topological and chemically, in response to reaction conditions exposing a new paradigm in the catalyst structure during operation.

Potassium and cobalt double-doped ferrierites as a new class of soot oxidation catalysts

Research efforts to develop an effective soot oxidation catalyst have intensified in recent years due to the increased awareness of the highly harmful effect of soot particles on the human health and the environment. Large-scale application of a developed catalyst calls for a cheap support material allowing for an effective dispersion and thus a decrease in the active phase loading. Zeolites, widely used in catalysis as active phase carriers, possess advantageous characteristics such as a uniform porous structure and large surface area. Furthermore, they are characterized by high availability, good price, and are environmentally friendly. Cobalt-based materials provide promising soot oxidation catalyst phases, and alkali doping can further enhance their activity. This study focuses on the optimization of the potassium loading in the potassium and cobalt double-doped ferrierites towards a new class of cheap and environmentally friendly soot combustion catalysts. The potassium doping of the ferrierite-supported cobalt spienel was optimized in the range of 0–14 wt%. The obtained materials were characterized in terms of their composition (XRF, XPS, XRD, Raman spectroscopy), morphology (SEM, TEM/EDX/FFT), and reducibility (H2-TPR), and tested in the process of soot oxidation in tight and loose contact modes. The strong promotional effect of potassium was discussed in terms of a significant modification of the catalyst electronic properties (work function studies) and supported by the potassium surface state studies by the alkali thermal desorption method (SR-TAD). It was found that the optimal potassium promoter dispersion leads to the lowest catalyst work function and its highest activity in soot combustion. The effect of nitric oxide was also investigated for selected catalysts. The opposite effect of NO on the activity of undoped and K-doped catalysts was discussed on the basis of in-depth spectroscopic studies. An enhanced formation of nitrate species was found on the surface of the K-containing catalyst which led to the stronger inhibiting effect of NO.

Low temperature multi-catalytic growth and growth mechanism of carbon nanotubes on carbon fiber surfaces

In order to reduce the etching effect of the catalysts to carbon fibers caused by high temperature during the chemical vapor deposition (CVD) process, four multi-element catalysts, Fe–Co, Fe–Ni, Co–Ni and Fe–Co–Ni, were used to realize the low temperature growth of carbon nanotubes (CNTs) on carbon fibers at 350 °C–400 °C. The results show that the growth state of CNTs has a great relationship with the type of catalysts. The catalytic efficiency of Fe–Co catalysts is low, but the graphitization degree of CNTs is relatively high. The Fe–Co–Ni catalysts has high catalytic efficiency but low graphitization degree of CNTs. The tensile strength of carbon fiber/CNTs reinforcements prepared by Fe–Ni catalysts at 400 °C is the highest, reaching 3.99 GPa, which is 11.14% higher than that of desized fiber. The melt drop phenomenon of the catalysts was found by TEM, indicating the formation of the liquid phase catalysts during the growth of CNTs. This phenomenon can change the diffusion mode of carbon atoms in the catalyst and significantly reduce the growth activation energy of CNTs, so that CNTs can grow at lower temperatures. Based on the detailed analysis of the CVD process, a low temperature growth model of CNTs on carbon fibers was proposed.

Role of promoters over yttria‐zirconia supported Ni catalyst for dry reforming of methane

AbstractDry reforming of methane (DRM) bears great hope for the catalytic community as well as environmentalists for its potential to convert two greenhouse gases, CH4 and CO2, together into synthetic feedstock “syngas”. The stable tetragonal zirconium yttrium oxide phase over the “Yttria‐zirconia supported Ni” catalyst (Ni/YZr) brings &gt;70% CH4 conversion against 50% CH4 conversion over zirconia supported Ni catalyst) in 7 h time‐on‐stream (TOS). The use of the second metal oxide (MOx; M = Ho, Ga, Gd, Ba, Cs) in a small amount (4 wt%) over Ni/YZ catalyst is found to promote the catalytic activity further. Herein, we have prepared such metal‐promoted yttria‐zirconia supported Ni catalyst, employed them for DRM and characterized them with surface area porosity, X‐ray diffraction, spectroscopic techniques, temperature programmed techniques and transmission electron microscopy. A fine correlation of characterization results with catalytic activity brings out various useful information that would be useful for establishing yttria‐zirconia supported Ni catalyst for DRM. Ni stabilized over cubic zirconium holmium oxide phase in 5Ni4Ho/YZr catalyst, cubic zirconium gadolinium oxide phase in 5Ni4Gd/YZr catalyst and cubic zirconium barium oxide phase in 5Ni4Ba/YZr catalyst perform excellent toward DRM. Catalytically, 5Ni4Ho/YZr catalyst achieves CH4 conversion as high as ~85% whereas 5Ni4Ba/YZr and 5Ni4Gd/YZr show CH4 conversions of about ~80%. Even in 30 h TOS study, 5Ni4Ho/YZr catalyst showed &gt;81% CH4 conversion with retaining highest H2/CO (0.97).

In2O3 Nanoparticles: An Ecofriendly and Reusable Nano-Catalyst for Green Synthesis of 1,8-dioxo-octa-hydro Xanthene Derivatives

A novel, singular, and reusable In2O3 nanocatalyst was synthesized in the laboratory using a hydrothermal process. The In2O3 catalyst was characterized via specific strategies like Fourier transform infrared (FT-IR) was used to study the functional groups present in the In2O3 catalyst. Energy-dispersive X-ray spectroscopy (EDS) was used to analyze the elemental composition of the catalyst. A scanning electron microscope (SEM) was used to observe the morphology of the catalyst at a microscale level. X-ray diffraction pattern (XRD) was used to determine the crystal structure of the catalyst, and data analysis confirmed the formation of the crystalline phase of the In2O3 catalyst. The synthesized In2O3 catalyst was used for the synthesis of 1,8-dioxo-octa-hydro xanthene derivatives with 94% yield within 15 min of workup, this makes it a cost-effective and sustainable option for future synthesis reactions. Overall, the synthesis of this novel In2O3 nanocatalyst and its successful application in the synthesis of 1,8-dioxo-octa-hydro xanthene derivatives highlights the potential of green chemistry approaches in developing efficient and environmentally friendly chemical processes.

Insights into the structural, and functionality of RuO2/TiO2 and Ni(OH)2/RuO2/TiO2 for water splitting and dye degradation

Heterogeneous catalysis and the uniform interface are playing a vital role in environmental protection and are amenable to photoelectrochemical transformation reactions. Herein, a mixed metal oxide catalyst composed of RuO2 or RuO2/Ni(OH)2 supported on TiO2 is developed via the facile sol-gel method. Structural and morphological analyses confirm the presence of RuO2 and Ni(OH)2 beside the anatase phase in the composite catalysts . The band gap of TiO2 is tuned after contacting with RuO2 (2.35 eV) and the surface area is doubled. XPS shows the existence of a high level of defects and VSM demonstrates a ferromagnetic-like hysteresis loop for TiRu. A fast positron annihilation is observed of TiRu compared to TiO2 indicating smaller free volume defects in the composite powders. The oxidation tests of water display a high current density of 18.6 mA/cm2 and dimensional stability for the TiRu sample with negligible electroactivity for TiRuNi. On the other hand, the photoelectrochemical water splitting activity is found to be the lowest for the composite samples compared to TiO2. The photocatalytic efficiency is further examined via the removal of two industrial dyes (Dianix Blue and Indigo Carmine dyes) and the performance is correlated to the results obtained from Mott-Schottky.

Microbial Fuel Cell Using a Novel Ionic Liquid-Type Membrane–Cathode Assembly for Animal Slurry Treatment and Fertilizer Production

The implementation of a microbial fuel cell for wastewater treatment and bioenergy production requires a cost reduction, especially when it comes to the ion exchange membrane part and the catalysts needed for this purpose. Ionic liquids in their immobilized phase in proton exchange membranes and non-noble catalysts, as alternatives to conventional systems, have been intensively investigated in recent years. In the present study, a new microbial fuel cell technology, based on an ionic liquid membrane assembly for CoCu mixed oxide catalysts, is proposed to treat animal slurry. The new low-cost membrane–cathode system is prepared in one single step, thus simplifying the manufacturing process of a membrane–cathode system. The novel MFCs based on the new low-cost membrane–cathode system achieved up to 51% of the power reached when platinum was used as a catalyst. Furthermore, the removal of organic matter in suspension after 12 days was higher than that achieved with a conventional system based on the use of platinum catalysts. Moreover, struvite, a precipitate consisting of ammonium, magnesium, and phosphate, which could be used as a fertilizer, was recovered using this membrane–cathode system.

Quantitative estimation of triple phase boundaries in solid oxide fuel cell electrodes via artificial neural network

Virtual solid oxide fuel cell (SOFC) electrode microstructures composed of pore, electrolyte and catalyst phases with various particle sizes and volume fractions are reconstructed to design high-performance electrodes by investigating the role of microstructural properties on the electrodes and thereby the cell performance. The active TPB (triple phase boundary) densities in these microstructures are numerically measured and the data are used to train numerous artificial neural networks established with different model parameters and learning methods. Based on the results of 10,000 trainings of each model, the network that employs a backpropagation method of Bayesian regulation and has 2 hidden layers with 15 neurons is found to be the best one. It is then used to simulate new cases, whose parameters are in the range of those used in training. Further validation of the best network is also performed by considering a few randomly selected cases. The simulation results providing active TPB densities quantitatively are discussed regarding the microstructural properties. The overall results reveal that active TPBs can be increased by reducing the particle size of the phases and volume fraction of any phase should be selected according to the particle size to improve the number of active TPBs.

Synthesis of Catalysts Containing Mixed Oxides of Mo‐V‐Cu‐W to Produce Acrylic Acid: A Comparison between Hydrothermal Synthesis and Coprecipitation

AbstractMixed oxides of Mo‐V‐W‐Cu were prepared by three different synthesis methods, namely, evaporation (EV), hydrothermal treatment (TH), and evaporation, followed by hydrothermal treatment (EV‐TH). The catalyst samples were characterized by X‐ray diffraction (XRD) and fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption/desorption techniques. Subsequently, their catalytic performance was evaluated for the oxidation of acrolein to obtain acrylic acid. The results revealed that the composition of the crystalline phases of the mixed oxide catalysts influences their catalytic performance, and this effect varies depending on the synthesis method. The catalysts synthesized by EV‐TH showed better catalytic results than catalysts synthesized solely via EV or TH methods. This improvement may be attributed to the higher content of vanadium oxides found in the samples of EV‐TH, along with the formation of V0.35Mo4.65O14 as the predominant crystalline phase.

Influence of A-site Deficiency and Ni/Co Ratio in B-site on Electrochemical Performance of (La0.25Sr0,25Ca0.45)yTi0.95Ni0.05-xCoxO3- d Anode

La0.25Sr0.25Ca0.45TiO3 -d (LSCT) is a perovskite (ABO3) type mixed ionic-electronic conductive (MIEC) oxide and has been proposed as an electrode material for high temperature fuel cell [1]. This material owing high conductivity, robustness in hydrocarbon fuels and significant amount of attention has been paid to improve the electrochemical activity [1, 2]. Doping of B-site with some d-metal cation (Ni, Co, Mn, V, Mo) has been demonstrated to improve the catalytic activity. One of the advantages of the MIEC conducting scaffold based electrodes is that the catalyst phase on the electrode surface can be kept to a minimum, usually less than 5 wt%, which minimizes any risks of physical damage during redox cycling [2].In this work, Ni/Co ratio and deficiency of A-site, of (La0.25Sr0.25Ca0.45)xTi0.95Ni0.05-yCoyO3 -d were varied. Electrical as well as electrochemical performance and chemical composition of LSCTNC surface was monitored. The electrochemical measurements of symmetric cells during 100 h tests show that small stochiometric changes in A-site significantly influence the activity and initial degradation rate of the electrode. The chemical and structural changes of the material surface have a key role on the electrochemical performance of the electrode [3].The electrode materials were analysed using XRD, TOF SIMS and electrochemical methods. XRD and TOF SIMS results for studied electrode powders showed significant dependence of the lattice parameters and electrode surface composition on the perovskite elemental composition. The results from impedance spectroscopy (measured at temperatures from 973 to 1123 K in H2 environment, at OCV) demonstrate a significant influence of the A-site deficiency and B-site composition on the electrochemical properties of studied electrodes. Robert Price, Mark Cassidy, Jan G. Grolig, Gino Longo, Ueli Weissen, Andreas Mai, John T. S. Irvine, Advanced Energy Materials, 11, 1 (2021). Paul A. Connor, Xiangling Yue, Cristian D. Savaniu, Robert Price, Georgios Triantafyllou, Mark Cassidy, Gwilherm Kerherve, David J. Payne, Robert C. Maher, Lesley F. Cohen, Rumen I. Tomov, Bartek A. Glowacki, Ramachandran Vasant Kumar, John T. S. Irvine, Advanced Energy Materials, 8, 1 (2018). Ove Korjus, Priit Möller, Kuno Kooser, Tanel Käämbre, Olga Volobujeva, Jaak Nerut, Sander Kotkas, Enn Lust, Gunnar Nurk, Journal of Power Sources, 494, 1 (2021).

First-Principles Studies for Optimal Model of the Ni/YSZ Triple Phase Boundary in Solid Oxide Cells

Non-Faradaic electrochemical modification of catalytic activity (NEMCA) with electric field applications in solid oxide cells (SOCs) is thought to be induced by spillover effects of lattice oxygen from the bulk, although the detailed mechanism has not still been clear. In SOCs, important phenomena such as fuel decomposition, charge transfer, etc. occur at the triple phase boundary (TPB) as a highly active site that consists of catalyst, electrolyte, and gas phases. NEMCA is expected to be also induced strongly by the surface mechanism on TPB, and understanding surface reactions on TPB is essential for improving catalyst and cell performances. However, the reliable TPB model has not been still uniquely defined to discuss the property of TPB although various studies have been reported. Therefore, in this study, we have focused on the TPB model comprising Ni catalyst cluster; YSZ electrolyte; and gas phase, and aimed to identify a reliable TPB model for theoretical studies by using first-principles calculations as an initial step. In concrete, we identified firstly the stable structures of YSZ surface models by using DFT calculations taking into account oxygen vacancy positions, yttrium atom arrangements, yttria concentration, and other factors. Thereafter, we discussed a reliable Ni/YSZ interface model based on the most stable YSZ model proposed above results by evaluating the Ni structure, interface stability, and so on.In this study, DFT calculations with a plane-wave basis set were implemented using CASTEP, and GGA-PBE exchange-correlation functional was used. The plane-wave cutoff energy was set as 489.8 eV, the OTFG-ultrasoft was used as the pseudopotentials, and the spin-polarization is considered because YSZ is a ferromagnetic substance. In YSZ surface models, yttria concentrations are set to 4.35 mol% and 9.1 mol% which shows the maximum ion conductivity of ZrO2. The three-layer YSZ (111) slabs with 15 Å vacuum layer with 2×2 and 2×4 unit cells were used for repeated slab models. The DFT+U method is used to obtain the correct electric structure of metal oxides with partially filled d or f-orbital shells, and k-points were set to 4×2×1. In Ni/YSZ interface models, we considered Ni cluster and Ni belt type models based on the most stable 2×4 YSZ surface model (9.1 mol%) proposed in this study. We also considered both cases of (111) and (100) facets for the contact interface. In the case of Ni/YSZ interface models, the DFT+U method was not considered to improve the calculation convergence and k-points were set to 4×2×1. A schematic diagram of the Ni/YSZ interface model is shown in the attached Figure.In the case of the 2×2 YSZ model with the yttria concentration of 9.1 mol%, the YSZ model is stabilized when oxygen vacancy is on the second O atom layer and the second neighbor to Y atoms, indicating that improvement in the geometry instability of ZrO2 for 8-coordination is more important than keeping local electron neutrality. We have also found that oxygen vacancy positions are more sensitive to the YSZ surface stability than Y atom arrangements. In the case of the 2×4 YSZ model with the yttria concentration of 4.35 mol%, the YSZ model where there are Y atoms on the first layer is stabilized. The crystal structure achieves a more stable structure by varying bond lengths when Y3+ with the larger ionic radius is replaced with Zr4+. Therefore, the structure is easier to stabilize when the Y atom exists on the surface than in the bulk due to the higher degree of freedom of the Y atom. The most stable structure of the 2×4 YSZ model with the yttria concentration of 9.1 mol% given based on the above results is 0.18 eV more stable than the previously reported structure [1]. This is because the number of Y atoms on the first layer with the second neighbor from oxygen vacancy is larger than the previously reported structure. We evaluated then the structural stability of the Ni/YSZ interface model based on the above YSZ model. As a result, we have found that adhesion energy between Ni and YSZ is independent of the relative position of Ni atoms. In addition, the larger the number of Ni atoms is, the more stable the structure is. This is because the electronic property of Ni atoms approaches the metal as increasing the number of Ni atoms. Other results and a detailed discussion will be reported in our meeting publications (ECS Transactions) and the presentation.[1] M. Shishkin and T. Ziegler, Phys. Chem. Chem. Phys., 16, 1798-1808 (2014). Figure 1

Commercial SCR catalyst modified with Cu metal to simultaneously efficiently remove NO and toluene in the fuel gas.

Developing an environmentally friendly selective catalytic reduction (SCR) catalyst to effectively eliminate both nitric oxides (NO) and toluene has garnered significant attention for regulating emissions from automobiles and the combustion of fossil fuels. This study synthesized a series of novel commercial V2O5-WO3/TiO2 catalysts modified with Cu through the wet impregnation method, which was employed to simultaneously remove NO and toluene from the fuel gas. The assessment of catalyst removal performance was conducted at a selective catalytic reduction system, and the experimental results showed a significant increase in the catalytic activity due to the modification of the copper metal. The 10% Cu/SCR catalyst showed a superior activity that the NO and toluene conversion reached 100% and 95.56% at 300 °C, respectively. Subsequently, various characterization techniques were employed to investigate the crystal phase, morphology, physical features, chemical states, and surface acidity properties of the synthesis catalysts. According to the characterization results, the presence of Cu metal did not have a noticeable impact on the physical property. However, the redox performance was enhanced, and the number of surface acidic sites was also increased after adding Cu to the SCR catalyst. Furthermore, the redox cycle of Cu metal and V species was facilitated to produce more active oxygen which helped to improve the NO and toluene conversion. This work offered a novel perspective into the synergistic oxidation of both NO and toluene, which was potentially relevant for improving the selective catalytic reduction process in coal-fired power plants.

Unexpectedly Enhanced Organics Removal in Persulfate Oxidation with High Concentration of Sulfate: The Origin and the Selectivity.

Massive anions in high saline wastewater are primary factors that restricted the efficiency of pollutant degradation in advanced oxidation processes (AOPs). Herein, we reported the influence laws of different anions at high concentration on the electron-transfer process in the activation of persulfate, and especially, the sulfate anion exhibited the excellent promotion effect. Depending on the ionic charge, polarizability, and size, the anions exerted diverse effects on the dispersed phase and zeta potential of carbonaceous catalysts, which further embodied in the removal of pollutants. Based on the differences of reaction rate constant in water solution and high saline solution, the order was ClO4- < NO3- < Cl- < SO42- < CO32-, obeying the Hofmeister series. The enhancement of the sulfate anion was widely confirmed with different carbonaceous catalysts and pollutants with various structures. It could be attributed to the higher oxidation capacity, the faster interfacial electron transfer, and the better catalyst dispersion in the high sulfate environment. On the other hand, the decrease of zeta potential of the catalyst induced by sulfate reinforced the electrostatic attraction or repulsion with pollutants, which caused the selectivity of the sulfate promotion effect. Overall, this study provides new insights into the mechanism of influence of anions on AOPs, which refreshed the cognition of the role of sulfate on pollutant degradation, and helps guide the treatment design of high salinity wastewater.

Genesis of Active Phase and Support Effect in Ultradispersed Mo Sulfide Catalysts

Genesis of Active Phase and Support Effect in Ultradispersed Mo Sulfide Catalysts

MgAl2O4 with CaO in supported Ni and Ni–Co catalysts – impact on CO2 reforming of CH4

ABSTRACT To obtain insight into the effect of promoter–support interactions in CO2 reforming of CH4, a series of Ni and Ni–Co (3:1) catalysts were prepared over modified-MgAl2O4 and MgAl2O4. The prepared samples were characterised and investigated for dry reforming of methane reactions at 873 K and 1 atm. From XRD, it appears that CaO, in a specified amount, is an appropriate modifier to retain the active metallic phase of catalyst and also prevents the formation of a solid solution of itself with the metal oxides during catalyst synthesis. From activity results, enhancement in catalytic activity was observed for Ni and Ni–Co catalysts supported over modified-MgAl2O4 support due to the presence of new and more number of active metal sites. For 100Ni–2.5CaO/MgAl2O4 catalyst, initial CH4 conversion was 1.3 times greater than 100Ni/MgAl2O4. For Ni–Co catalysts comparable results were observed over modified-MgAl2O4 and MgAl2O4 supports. Moderately active carbon species were formed during dry reforming of methane reaction and the presence of new and more number of basic sites helped to minimise carbon deposition. Highlights Incorporation of a metal oxide in appropriate composition proves to be more chemically active than MgAl2O4 Ni–Co synergy exhibited higher catalytic activity Formation of new adsorption site due to support modification Improvement in H2: CO ratio was observed after addition of CaO Similar kind of carbon formation over both the series and Methane decomposition reaction is the source