A durable and robust Fe–N–C electrocatalyst for oxygen reduction reactions by introducing Ti3C2–TiO2 as radical scavengers

Modern Fe–N–C electrocatalysts are promising as alternatives to expensive Pt-based catalysts for oxygen reduction reactions (ORR). Although the activity of this type of electrocatalyst have been improved over the years, their durability and longevity need critical enhancements for practical applications in fuel cells. Typically, the incomplete oxygen reduction inevitably generates reactive oxygen species, including ·OH and HO₂· radicals, which will fiercely attack the carbon support and directly damage active sites in Fe–N–C electrocatalysts. Herein, a durable and robust Fe–N–C@Ti₃C₂–TiO₂ electrocatalyst for high-efficiency ORR is synthesized, in which Ti₃C₂–TiO₂ could effectively scavenge ·OH radicals or decompose H₂O₂ molecules, and synergistically work with Fe–N–C catalysts to improve the durability. Consequently, the Fe–N–C@Ti₃C₂–TiO₂ electrocatalyst shows prominent ORR performance in both alkaline and acidic electrolytes, low H₂O₂ yield, and long-term stability. This work provides great prospects for the design of highly stable ORR electrocatalysts by introducing radical scavengers as an active defense to proactively eliminate H₂O₂ and its radicals.     

Conversion of hydrogen/carbon dioxide into formic acid and methanol over Cu/CuCr2O4 catalyst

Cu/CuCr₂O₄ catalysts were prepared by impregnation method at various calcination temperatures (300, 400, and 500 °C) and then reduced in H₂ stream. The aggregated particles and decreasing surface area/pore volumes of the deactivated catalysts during HCOOH and CH₃OH formations were also observed. Particularly, the EXAFS data showed that first shells of Cu atoms transforms from Cu–O to Cu–Cu after catalytic reactions, their bond distances and coordination numbers are quite different, respectively. It revealed that metallic Cu atoms are one of the important active species over catalyst surface at different reaction temperatures having many unoccupied binding sites for HCOOH and CH₃OH formations. Additionally, the optimal calcination temperature for Cu/CuCr₂O₄ catalysts was demonstrated at 400 °C that attributed to its strongest acidity and basicity. The catalytic reactions in the duration of HCOOH and CH₃OH preparation were proposed that were composed of HCOOH formation, CH₃OH formation, and CH₃OH decomposition happening at CuCr₂O₄, Cu, and CuO active sites, respectively. The highest CO₂ conversion (14.6%), HCOOH selectivity/yield (87.8/12.8%), and TON/TOF values (4.19/0.84) were obtained at 140 °C and 30 bar in 5 h, respectively. Optimal rate constant (2.57 × 10^?2 min^?1) and activation energy (16.24 kJ mol^?1) of HCOOH formation were evaluated by pseudo first-order model and Arrhenius equation, respectively.     

Photofragmentation laser-induced fluorescence imaging in premixed flames

Two-dimensional measurements of primarily hydroperoxyl radicals (HO₂) are, for the first time, demonstrated in flames. The measurements are performed in different Bunsen-type premixed flames (H₂/O₂, CH₄/O₂, and CH₄/air) using photofragmentation laser-induced fluorescence (PF-LIF). Photofragmentation is done by laser radiation at 266 nm, and the generated OH photofragments are probed through fluorescence induced by a laser tuned to the Q₁(5) transition at 282.75 nm. The signal due to naturally occurring OH radicals, recorded by having the photolysis laser blocked, is subtracted, providing an image that reflects the concentration of OH fragments generated by photolysis, and hence the presence of primarily HO₂, but also smaller contributions from H₂O₂ and, for the methane flames, CH₃O₂. For the methane flames the measured radial profiles of OH photofragments and natural OH agree well with corresponding profiles calculated for laminar, one-dimensional, premixed flames using CHEMKIN-II with the Konnov detailed C/H/N/O reaction mechanism. An interfering signal contribution is observed in the product zone of the methane flames. It is concluded that the major source for the interference is most likely hot CO₂, from which O atoms are produced by photolysis, and OH is rapidly formed as the O atoms react with H₂O and H₂. This conclusion is supported by the fact that the interference is absent for the hydrogen flame, but appears when CO₂ is seeded into the flame. Another strong indication is that the Konnov mechanism predicts a similar buildup of OH after photolysis.     

The special route toward conversion of methane to methanol on a fluffy metal-free carbon nitride photocatalyst in the presence of H2O2

A fluffy mesoporous graphitic carbon nitride (g-CN) was synthesized and investigated, as the first metal-free polymeric semiconductor photocatalyst, for partial oxidation of methane to methanol at a mild condition (35°C) in the presence of hydrogen peroxide (H₂O₂). The addition of g-CN photocatalyst enhanced the methanol production with H₂O₂ by 10 times under visible light and this production was 3-folds that when WO₃ was used. Besides, while attaining a comparable saturated production of CH₃OH, the visible-light-driven reactions allowed a higher utilization ratio of H₂O₂ compared with those under the irradiation of simulated AM1.5G sunlight. More importantly, via electron spin resonance technique, scavenger experiments and isotope tracer investigations, as well as studies on the effects of reaction condition variations, the specific reaction mechanisms were revealed under both visible light and simulated full sunlight, respectively, which should shed some new insights on photocatalytic oxidation of CH₄ to value-added chemicals.     

Amine group ligand-modified hydrotalcite-like nano cobalt hydroxide for efficient oxygen evolution reaction

The advancement of highly-efficient, non-noble metal electrocatalysts with high active sites for oxygen evolution reaction (OER) continues to face severe challenges. In this work, a new 3D flower-like α-Co(OH)₂ catalyst with high Co–NH₂ active sites (referred to as α-Co(OH)₂–NH₂) is prepared. The Co–NH₂ active sites are formed through the interactions between Co²⁺ and –NH₂ groups and exhibit higher electrocatalytic performance for OER in alkaline mediums, with a lower overpotential (300 mV at 10 mA cm⁻²), a flatter Tafel slope (75 mV dec⁻¹) and a longer stability. Moreover, water splitting catalyzed by α-Co(OH)₂–NH₂ delivers 1.62 V to reach a current density of 10 mA cm⁻². The mechanism studies show that the OER electrocatalytic activity is closely related to the content of –NH₂. Density functional theory (DFT) calculations unveil that –NH₂ groups can facilitate the formation of OH1 on the α-Co(OH)₂ surface and promote the desorption of O₂1 into O_2(g).     

Engineering the performance of heterogeneous WO3/fullerene@Ni3B/Ni(OH)2 Photocatalysts for Hydrogen Generation

The hydrogen production through solar water splitting could be eco-friendly, environmental-benign and sustainable, alternative to fossil fuels energy carriers. In this work, the novel heterojunction WO₃/fullerene/Ni₃B/Ni(OH)₂ composites were successfully fabricated through different methods. The Ni₃B/Ni(OH)₂ as a needle like nanostructures were integrated into the interfaces between WO₃ and fullerene. The structural phase and morphology of prepared nanomaterials were significantly modified by incorporating the Ni₃B/Ni(OH)₂ as a co-catalyst. The results demonstrated that dopant element serves as the conductive electron bridges, rather than general cocatalyst, to accumulate electrons and inspire the H₂ generation kinetics over pure WO₃ photocatalyst. The significantly improved hydrogen rate of evolution up to 1578 μmol h⁻¹ g⁻¹ was found for hybrid photocatalyst [WO₃/fullerene@ 1.5% Ni₃B/Ni(OH)₂] which was 9.6 times higher as compared to pure photocatalyst. The interfacial contact between co-catalyst and composite could play substantial role in effective separation and transference of charge-carriers for improved hydrogen evolution rate. Under the visible light illumination, the heterojunction nanostructures inspire rapid transfer of electrons from WO₃ towards Ni₃B/Ni(OH)₂ to inhibit the fast recombination rate and prolong the WO₃ charge-carrier's lifetime, thereby releasing more electrons with greater reducing power for hydrogen production. This work may open an avenue for the strategy and green preparation of robust photocatalysts for scalable applications in solar H₂ evolution and sustainable environment.     

Zirconia-supported tungsten oxides for cyclic production of syngas and hydrogen by methane reforming and water splitting

ZrO₂-supported tungsten oxides were used for cyclic production of syngas and hydrogen by methane reforming (reduction) and water splitting (re-oxidation). The reduction characteristics of WO₃ to WO₂ and WO₂ to W were examined at various temperatures (1073–1273 K) and reaction times. Significant portions of the tungsten oxides were also reduced by the produced H₂ and CO. The extent of reduction by H₂ varied greatly depending on temperature and WO₃ content and also on the reduction of either WO₃ or WO₂, while that by CO was consistently low. When the overall degree of reduction became sufficiently high, methane decomposition started to proceed rapidly, resulting in considerable carbon deposition and H₂ production. Consequently, the H₂/(CO + CO₂) ratio varied from around 1 to higher than 2. During the repeated cyclic operations with a proper reduction time at a given temperature, the syngas and hydrogen yields decreased gradually while the H₂/(CO + CO₂) ratio remained nearly constant and the carbon deposition was negligible.     

Mechanisms insight into oxygen reduction reaction on sulfur-doped Fe–N2 graphene electrocatalysts

The density functional theory (DFT) calculations were performed to investigate the stability of the S-doped Fe–N₂G electrocatalysts, as well as ORR mechanism and activity. The most stable configuration is the Fe–N₂S1G because of forming a strong bond structure of Fe–S. In addition, the structures of Fe–N₂S3G and Fe–N₂S4G also exhibit the higher stability compared to the undoped Fe–N₂G. According to the distinct charge difference on the surface, the O-contained intermediates would like to adsorb on the active sites of Fe–N₂ complex active sites. The binding strength of OH on these different catalysts follows the increasing order of Fe–N₂S4G < Fe–N₂S3G < FeN₂G < Fe–N₂S1G < Fe–N₂S5G < Fe–N₂S2G < Fe–N₂S6G < Fe–N₂S7G, implying the opposite order of the catalytic activity. The calculations of the free energy diagrams show that all elementary reaction steps on Fe–N₂S4G, Fe–N₂S3G, FeN₂G and Fe–N₂S1G are downhill. Besides, the rate determining step (RDS) for these catalysts (excluded Fe–N₂S4G) is the fourth reduction step (OH*+H⁺+e⁻→H₂O+*). The study of the reaction mechanisms predicted that the direct 4-electron reduction process is the favorable ORR pathway, and the alternative reaction pathways containing the formation of OH* + OH* co-adsorbate also process without the formation of H₂O₂ for these catalysts. Particularly, Fe–N₂S4G also exhibits the outstanding performance for H₂O₂ reduction. In general, since the higher stability and working potential for ORR, Fe–N₂S4G is predicted to be the prior candidate site for ORR among S-doped FeN₂G catalysts.     

Density functional theory study of the copper phthalocyanine based metal−organic frameworks as the highly active electrocatalysts for the oxygen reduction

Recently, the copper phthalocyanine based 2D conjugated MOFs have been demonstrated that it can efficiently catalyze the oxygen reduction reaction (ORR) experimentally. Herein, the inherent properties and ORR mechanism of PcCu-O₈-M (M = Fe, Co, Ni, Cu) containing two potential active sites (M–O₄ and Cu–N₄ sites) are investigated by density functional theory methods. The binding energy of oxygen-containing intermediates on PcCu-O₈-M indicates that the binding strength of 1OOH, 1O, and 1OH at the M–O₄ site is more moderate than that at the Cu–N₄ site. For all studied sites, their potential-determining steps are the step of O₂ → 1OOH except for the Ni–O₄ site of PcCu-O₈-Ni (1OH → H₂O). Among all sites of PcCu-O₈-M, the Fe–O₄ and Co–O₄ sites have excellent ORR activity with the overpotentials of 0.46 and 0.49 V, respectively, and the Cu–N₄ site of PcCu-O₈-Co possesses the relatively high ORR activity with the overpotential of 0.79 V. It can be concluded that compared with the Cu–N₄ site, the M–O₄ site plays major role for each PcCu-O₈-M during the ORR process. Moreover, the charge analysis of PcCu-O₈-Co suggests that the ORR activities of the Co–O₄ and Cu–N₄ sites are mainly originated from metal atoms (Co atom and Cu atom) as well as the O and N atoms (O and N-1) coordinated with metal atoms. In addition, PcCu-O₈-Co has high poisoning-tolerance ability to NO, NH₃, CO, SO₂, and H₂S.     

Understanding active sites and mechanism of oxygen reduction reaction on FeN4–doped graphene from DFT study

First-principle density functional theory (DFT) calculations are performed to study the active sites in FeN₄G electrocatalysts, as well as ORR activity and mechanism. The possible intermediates and transition states existing in the possible reaction paths from Langmuir-Hinschelwood (LH) mechanism are investigated. The results show that the associative pathways of OOH1 formation is prior to that of O₂1 dissociation. The condition of proton adsorbed on top N sites (T2) is more beneficial to the reduction of O-contained species adsorbed on top Fe site (T1) compared to the conditions of proton adsorbed on top C sites (T3). However, the dissociation of O₂1, OOH1 and H₂O₂1 is more likely to occur on the paired T1-T3 sites, since their lower energy barriers compared to other paired sites. The most favorable four-electron reduction pathway follows the mechanisms: O₂1→ OOH1→ O1+H₂O→ OH1+H₂O→ 2H₂O. The rate determining step for ORR on FeN₄G is the reduction of O1 into OH1 (barrier, 0.47 eV). The most feasible pathway for ORR is downhill at a high electrode potential (0.76 V vs. SHE at pH = 0) according to the free energy diagram. Compared to the ideal catalyst, the adsorption energy of OOH1 on FeN₄G is much lower in free energy, while those of OH1 and O1 are slightly higher. Additionally, the elementary reaction rate for OOH1→O1+H₂O is much larger than that of OOH1→H₂O₂ based on the parameter of activation barrier. Therefore, the formation of H₂O₂ (l) is unfavorable on FeN₄G catalysts.     

A comparative study of ZrO2, Y2O3 and Sm2O3 promoted Ni/SBA-15 catalysts for evaluation of CO2/methane reforming performance

Ni-based/SBA-15 catalysts, were promoted by 3wt % of samaria (Sm₂O₃), Yttria (Y₂O₃) and Zirconia (ZrO₂), by two-solvent impregnation method. The catalysts characterization was performed by N2 adsorption–desorption, X-ray Diffraction (XRD), X-ray Fluorescence (XRF), High Resolution Transmission Electron Microscopy (HRTEM), Field Emission Electron Scanning Microscopy (FESEM), Temperature Programmed Oxidation/Reduction (TPO/TPR) and NH₃-Temperature Programmed Desorption (NH₃-TPD) techniques. Then, evaluated by CO₂/methane reforming.The CO₂/methane reforming outcomes revealed that samaria-promoted catalyst showed excellent activity, stability and cock resistance, while yttria-promoted catalyst just illustrated good activity at high temperature and zirconia-promoted catalyst didn't show any modification in catalytic performance in comparison to Ni-based catalyst with no promoter. Samaria-promoted TEM and TPR analysis, indicated adding samaria improved the NiO particles interaction with SBA-15 support pores wall and NiO dispersion. The TPO analysis displayed that coke deposition in samaria-promoted sample after 12 h reaction is less than yttria-promoted during stream of 5 h. Also, it is suggested that for samaria containing catalyst, cock deposition occurred on the support. Therefore, nickel active sites were preserved for time on stream of 12 h, which is the main reason for samaria-promoted catalyst superior stability than other's.     

Tuning the hydrogen storage properties of MOF-650: A combined DFT and GCMC simulations study

Combined density functional theory and grand canonical monte Carlo (GCMC) calculations were performed to study the electronic structures and hydrogen adsorption properties of the Zn-based metal-organic framework MOF-650. The benzene azulenedicarboxylate linkers of MOF-650 were substituted by B atoms, N atoms, and boronic acid B(OH)₂ linkers, and the Zn atoms were substituted by Mg and Ca atoms. The calculated electronic densities of states (DOSs) of MOF-650 showed that introduction of B atoms reduces the band gap but damages the structure of MOF-650. Introduction of single N bonds cannot provide active electrons to attract H₂ molecules. Thus, substitutions of B and N into MOF-650 are not suggested. B(OH)₂ substitute in MOF-650 decreased its band gap, slightly improved its hydrogen storage ability and made H₂ molecules more intensively distributed besides organic linkers. GCMC calculations were carried out by estimating the H₂ storage amount of the pure and modified MOFs at 77 and 298 K and from 1 bar to 20 bar. B(OH)₂ linker and Mg/Ca co-doped MOF-650 showed increased H₂ adsorption by approximately 20 wt%. The adsorption of H₂ around different bonds showed the order N–C < C = C < B–C < C–O < B–O.     

A single tiny Tin(O2)n cluster decorated an ultra-small boron nitride nanotube for hydrogen storage material: A density functional theory study

The adsorption of hydrogen (H₂) on tiny titanium dioxide Ti_n(O₂)_n clusters where n = 1, 2 and 3 decorated a (5, 5) ultra-small boron nitride nanotube (BNNT) is studied theoretically using the density functional theory calculation. Ti_n(O₂)_n/BNNT is very stable and it can hold a large number of H₂ molecules while maintaining its stability. That H₂ adsorption on Ti_n(O₂)_n/BNNT/BNNT shifts the geometry of Ti_n(O₂)_n/BNNT as the number of H₂ molecules adsorbed on its surface increased. For example, the bond between N–O increases while the bond between the H atoms in the H₂ molecules shortens. Furthermore, the local density of states (LDOS), crystal orbital overlaps population (COOP), and charge distribution analysis all confirm that H₂ formed a bond with TiO₂/BNNT. Thus, we can conclude that Ti_n(O₂)_n/BNNT is a promising material for hydrogen storage.     

New insights into the interfacial interactions of O2 and H2O molecules with PuH2 (110) and (111) surfaces from first-principles calculations

The interfacial reaction of highly active plutonium hydride in humid circumstance is of great interest in nuclear safe handling and storage, but it is poorly understood so far. In this paper, we first studied the O₂ adsorption on (110) and (111) surfaces of PuH₂ by first-principles DFT + U method. The results show that there are dissociative and non-dissociative adsorption of oxygen on the surfaces. We analyze the vibrational frequencies of non-dissociative oxygen adsorbed on the surfaces. It is found that the corresponding frequency of oxygen with bond length of 1.330–1.340 Å is 1094.8–1098.2 cm^?1. The corresponding frequency of oxygen with bond length of 1.448–1.500 Å is 726.3–905.2 cm^?1. It shows that non-dissociative oxygen could be considered as superoxide (O₂^?) or peroxide (O₂^2?) species. In order to expound the atomistic evolution process of oxidized surface exposed to moist air or corrosive solution, the interactions between H₂O molecules and the strongest oxygen adsorption structures were further explored. The results indicate that H₂O molecules could dissociate into OH groups and H atoms, then they were captured to create Pu–O and H–O bonds. This work could provide new insights into the adsorption morphology of oxygen on hydride surface and the interaction between oxide/hydride interface and water.     

Ammonia and borane activation by Tantalum Carbide cluster anion Ta2C4−: A theoretical approach

Activation of C–H, B–H as well N–H sigma bonds has been a subject of fundamental interest due to potential feedstock in chemical industry. The co-operative effect of the metal centers in a di-nuclear carbide cluster Ta₂C₄^? for methane C–H activation and dissociation has recently been revealed, in which a molecule of hydrogen is evolved. Based on that, we have explored reaction pathways for ‘E?H’ sigma bond activation and dissociation processes of gaseous Ammonia (E: N) and Borane (E: B) using the stable form of the aforesaid complex at DFT levels. The geometries and energetics associated with the reactions are found to be method insensitive. The course of the reaction is initiated by a 1:1 precursor complex formed between the cluster and N (/B)H₃. This complex formation is found to be more exothermic than that of its methane counterpart. In case of BH₃, considerable lengthening of two B–H bonds in the first step is observed which implies that the two B–H bonds are activated simultaneously under the influence of Ta₂C₄^?. But for NH₃, N–H bond lengthening as well as activation is observed to be insignificant in this precursor complex. The chemical nature of the participating hydrogen atoms is inspected by NPA analysis (‘protic’ type in NH₃ and ‘hydride’ type in BH₃).The overall dehydrogenation procedures for both the molecules are found to be multi-step with high exothermicity. Highly negative net energy change in terms of Gibbs Free Energy (?31.03 kcal/mol for ammonia and ?31.36 kcal/mol for borane) as well as Enthalpy (?33.68 kcal/mol for ammonia and ?34.13 kcal/mol for borane), in forming a H₂ molecule with stable Ta₂C₄N(/B)H^? complex, with respect to the reactant pair govern the thermodynamic feasibility of the overall process. In a nutshell, this computational study provides a detail understanding of the activation and dissociation processes of the concerned gaseous molecules, which will be beneficial for further experimental studies.     

Effects of binary Co–Mn oxides promoters on low-temperature catalytic performance of Pd/Al2O3 for methane combustion

Aiming at fabricating high-activity and stable methane combustion catalysts in the dry/wet conditions, Co–Mn binary oxides were employed as promoters to Pd/Al₂O₃ system herein. The introduction of appropriate amount of manganese made Mn³⁺ maximally enter into the Co₃O₄ spinel structure, conducive to the conversion of Co³⁺ to Co²⁺ by Mn³⁺ and then the enhancement of lattice distortion. Therefore, abundant oxygen vacancies were produced, which enhanced the surface-concentrations of active Pd²⁺ and O_ads species, together with the exchange of oxygen species. The resulting catalyst with a molar Mn/Co ratio of 0.20 performed superior low-temperature activity and durability. Moreover, the synergy of Mn and Co could accelerate the removal process of accumulated OH/H₂O from the active sites, thereby promoting the regeneration of PdO and oxygen vacancies. This endowed the tailored catalyst with remarkable moisture-tolerance and hydrothermal stability, and inspiring enhanced activity (T₉₀ = 350 °C) after removing water vapor.     

Methane steam reforming for producing hydrogen in an atmospheric-pressure microwave plasma reactor

A methane steam reforming process for producing mainly hydrogen in an atmospheric-pressure microwave plasma reactor is demonstrated. Nano carbon powders, CO_x, C₂H₂, C₂H₄, and HCN were also formed. Intermediates such as OH, NH, CH, and active N₂ were identified using optical emission spectroscopy. The selectivity of H₂ was greater than 92.7% at inlet H₂O/CH₄ molar ratio (R) ≧ 0.5, and was higher than that obtained using methane plasmalysis because steam inhibited the formation of C₂H₂. The highest methane conversion was obtained at R = 1, reaching 91.6%, with the lowest specific energy consumption of H₂ formation at [CH₄]_in = 5%, 1.0 kW, and 12 slpm. The plasma-assisted catalysis process, which packed Ni/Al₂O₃ catalysts in the discharge zone and supplied heat using hot effluents, was used to elevate the methane conversion and hydrogen selectivity. However, large amounts of 40–70 nm carbon powder, which is electrically conductive, were produced, resulting in rapid catalyst deactivation due to carbon being deposited on the surface and in the pores of catalysts.     

Highly selective hydrogen sensing of Pt-loaded WO3 synthesized by hydrothermal/impregnation methods

Unloaded and 0.25–1.0 wt% Pt-loaded WO₃ nanoparticles were synthesized by hydrothermal method using sodium tungstate dihydrate and sodium chloride as precursors in an acidic condition and impregnated using platinum acetylacetonate. Pt-loaded WO₃ films on an Al₂O₃ substrate with interdigitated Au electrodes were prepared by spin-coating technique. The response of WO₃ sensors with different Pt-loading concentrations was tested towards 0.01–1.0 vol% of H₂ in air as a function of operating temperature (200–350 °C). The 1.0 wt% Pt-loaded WO₃ sensing film showed the highest response of ∼2.16 × 10⁴ to 1.0 vol% H₂ at 250 °C. Therefore, an operating temperature of 250 °C was optimal for H₂ detection. The responses of 1.0 wt% Pt-loaded WO₃ sensing film to other flammable gases, including C₂H₅OH, C₂H₄ and CO, were considerably less, demonstrating Pt-loaded WO₃ sensing film to be highly selective to H₂.     

The role of hydrogen bronzes in the hydrogenation of polyfunctional reagents: cinnamaldehyde,furfural and 5-hydroxymethylfurfural over Pd/HxWO3 and Pd/HxMoO3 catalysts

Differences in the activity of Pd/WO₃ and Pd/MoO₃ (Pd loading 0.4–4 wt%) catalysts in competitive hydrogenations of the CC and CO groups in polyfunctional reagents have been studied as a function of two effects: (1) the in situ formation of hydrogen bronzes, H_xWO₃ and H_xMoO₃, and (2) the electronic interaction between the supports and the metallic Pd. The cinnamaldehyde (CAL), furfural (FU) and 5-hydroxymethylfurfural (HMF) were hydrogenated under mild reaction conditions. The formation of hydrogen bronzes in Pd/WO₃ and physical mixture of Pd/WO₃ with supporting WO₃ oxide upon exposure to H₂ was also studied using the gas flow-through microcalorimetry. In both Pd/MoO₃ and Pd/WO₃ catalysts, the electronic interactions contributed to the promotion of selectivity toward the CO hydrogenation in CAL and FU, yet in Pd/MoO₃ this effect was much more pronounced. On the other hand, apart from increasing the overall reaction rate, the formation of hydrogen bronzes remarkably enhances the CC hydrogenation in CAL, as well as the decarbonylation of FU to furan and hydrogenolysis of C–OH in HMF to 5-methylfurfural. The bronze effects are significantly stronger in H_xWO₃, compared to H_xMoO₃, which may be related to higher H-species mobility and weaker H-bonding in the W–O–H (54 kJ/mol H₂) than in the Mo–O–H (100 kJ/mol H₂). This may also explain very high tendency of Pd/WO₃ to furan ring hydrogenation in FU and HMF as well as almost selective (>98%) hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol.     

W-doped ordered mesoporous Ni–Al2O3 catalyst for methanation of carbon monoxide

In order to simultaneously inhibit the Ni sintering and coke formation as well as investigate the effects of WO₃ promoter on catalytic performance, the ordered mesoporous Ni–WO₃/Al₂O₃ catalysts were synthesized by a facile one-pot evaporation-induced self-assembly method for CO methanation reaction to produce synthetic natural gas. Addition of WO₃ species could significantly promote the catalytic activity due to the enhancement of the Ni reducibility and the increase of active centers, and the optimal N10W5/OMA catalyst with NiO of 10 wt% and WO₃ of 5 wt% achieved the maximum CH₄ yield 80% at 425 °C, 0.1 MPa and a weight hourly space velocity of 60000 mL g⁻¹ h⁻¹. Besides, the reference catalyst N10W5/OMA-Im prepared by the conventional co-impregnation method was also evaluated. Compared with N10W5/OMA, N10W5/OMA-Im showed lower catalytic activity due to the partial block of channels by Ni and WO₃ nanoparticles, which reduced active centers and restrict the mass transfer during the reaction. In addition, the N10W5/OMA catalyst showed superior anti-sintering and anti-coking properties in a 425^oC-100 h-lifetime test, mainly because of confinement effect of ordered mesoporous structure to anchor the Ni particle in the alumina matrix.