Mapping the Catalytic-Space for the Reactivity of Metal-free Boron Nitride with O2 for H2O-Mediated Conversion of Methane to HCHO and CO

Transition-metal based catalysts have been widely employed to catalyze partial oxidation of light alkanes. Recently, metal-free hexagonal-boron nitride (h-BN) has emerged as a promising catalyst for the oxidation of CH4 to HCHO and CO; however, the intricate catalytic surface of h-BN at molecular and electronic levels remains inadequately understood. Key questions include how electron-deficient boron atoms in h-BN reduce O2, and whether the partial oxidation of methane over h-BN exhibits similarities to traditional transition-metal catalysts. In our study, we computationally-mapped in-detail the surface catalytic-space of h-BN for methane oxidation. We considered different structures of h-BN and show that these structures contain numerous sites for O2 binding and therefore various routes for methane oxidation are possible. The activation barriers for methane oxidation via various paths varies from ~83 to ~123 kcal mol-1. To comprehend the differences in activation barriers, we employed geometrical, orbital and distortion/interaction analysis (DIA). Orbital analysis reveals that methane activation over h-BN in presence of dioxygen follows a standard hydrogen atom transfer mechanism. It is also shown that water plays an intriguing role in reducing the barrier for HCHO and CO formation by acting as a bridge.

Gas-Phase Selective Oxidation of Methane into Methane Oxygenates

Methane is an abundant resource and its direct conversion into value-added chemicals has been an attractive subject for its efficient utilization. This method can be more efficient than the present energy-intensive indirect conversion of methane via syngas, a mixture of CO and H2. Among the various approaches for direct methane conversion, the selective oxidation of methane into methane oxygenates (e.g., methanol and formaldehyde) is particularly promising because it can proceed at low temperatures. Nevertheless, due to low product yields this method is challenging. Compared with the liquid-phase partial oxidation of methane, which frequently demands for strong oxidizing agents in protic solvents, gas-phase selective methane oxidation has some merits, such as the possibility of using oxygen as an oxidant and the ease of scale-up owing to the use of heterogeneous catalysts. Herein, we summarize recent advances in the gas-phase partial oxidation of methane into methane oxygenates, focusing mainly on its conversion into formaldehyde and methanol.

The Impact of 3-(trihydroxysilyl)-1-propanesulfonic Acid Treatment on the State of Vanadium Incorporated on SBA-15 Matrix

Bifunctional catalysts—e.g., those with acidic and redox sites—are of particular importance, especially in the cascade processes, including the one-pot transformation of glycerol to acrylic acid. In this study, we explore one aspect of the preparation of a vanadium-containing catalyst, which can be further modified with 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS). The state of vanadium species loaded on mesoporous ordered silica of SBA-15 type was investigated before and after treatment with TPS, which can also be applied for the generation of acidic centers. Two vanadium sources, i.e., ammonium metavanadate and vanadium(IV) oxide sulfate, were applied to generate redox sites on SBA-15. The structure of materials obtained was analyzed using N2 adsorption/desorption and XRD measurements. For the estimation of the amount of vanadium and characterization of its state, the following techniques were applied: ICP, UV-Vis, XPS, ESR and FTIR combined with pyridine adsorption. The treatment of vanadium containing SBA-15 with TPS was found to lead to the oxidation of V4+ to V5+ and the partial removal of vanadium species, leading to a decrease in the number of penta-coordinated vanadium species. These features should be taken into account in the design of bifunctional catalysts with vanadium-active centers and SO3H acidic sites coming from TPS.

Study on the selective oxidation of methane over highly dispersed molybdenum-incorporated KIT-6 catalysts

The isolated MoO_x species contribute to the highly selective formation of formaldehyde.

Partial oxidation of methane to formaldehyde over copper–molybdenum complex oxide catalysts

The Cu₃Mo₂O₉ catalyst forms formaldehyde selectively in the methane oxidation with O₂ in the presence of water.

Increasing the Efficiency of Optimized V-SBA-15 Catalysts in the Selective Oxidation of Methane to Formaldehyde by Artificial Neural Network Modelling

The present study investigates the possibility of improving the selective oxidation of methane to formaldehyde over V-SBA-15 catalysts in two different ways. In a classical approach of catalyst optimization, the in situ synthesis of V-SBA-15 catalysts was optimized with regard to the applied pH value. Among the set of catalysts synthesized, a higher amount of incorporated vanadium, a higher content of polymeric VOx species as well as a less ordered structure of the support material were observed by increasing the pH values from 2.0 to 3.0. An optimum in performance during the selective oxidation of methane to formaldehyde with respect to activity and selectivity was found over V-SBA-15 prepared at a pH value of 2.5. With this knowledge, we have now evaluated the possibilities of reaction control using this catalyst. Specifically, artificial neural network modelling was applied after the collection of 232 training samples for obtaining insight into the influence of different reaction parameters (temperature; gas hourly space velocity (GHSV); and concentration of O2, N2 and H2O) onto methane conversion and selectivity towards formaldehyde. This optimization of reaction conditions resulted in an outstanding high space-time yield of 13.6 kgCH2O∙kgcat∙h−1.

Direct conversion of methane to formaldehyde and CO on B2O3 catalysts

Direct oxidation of methane to value-added C₁ chemicals (e.g. HCHO and CO) provides a promising way to utilize natural gas sources under relatively mild conditions. Such conversions remain, however, a key selectivity challenge, resulting from the facile formation of undesired fully-oxidized CO₂. Here we show that B₂O₃-based catalysts are selective in the direct conversion of methane to HCHO and CO (~94% selectivity with a HCHO/CO ratio of ~1 at 6% conversion) and highly stable (over 100 hour time-on-stream operation) conducted in a fixed-bed reactor (550 °C, 100 kPa, space velocity 4650 mL g_cat⁻¹ h⁻¹). Combined catalyst characterization, kinetic studies, and isotopic labeling experiments unveil that molecular O₂ bonded to tri-coordinated BO₃ centers on B₂O₃ surfaces acts as a judicious oxidant for methane activation with mitigated CO₂ formation, even at high O₂/CH₄ ratios of the feed. These findings shed light on the great potential of designing innovative catalytic processes for the direct conversion of alkanes to fuels/chemicals.

Partial oxidation of methane to value-added C₁ products remains challenging due to the favorable formation of fully-oxidized CO₂. Here, the authors show supported B₂O₃ catalysts with tri-coordinated BO₃ units as the active site are highly selective in oxidizing methane to HCHO and CO.

One-Pot Synthesis of Renewable Phthalic Anhydride from 5-Hydroxymethfurfural by using MoO3 /Cu(NO3 )2 as Catalyst

Herein, a synthetic pathway to renewable phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) in one pot is reported. The commonly available catalysts MoO₃ and Cu(NO₃ )₂ play a crucial role in integrating the multiple steps of the reaction, namely decarbonylation of HMF to active furyl intermediate (AFI), oxidation of HMF to maleic anhydride (MA), Diels-Alder cycloaddition of AFI and MA, and subsequent dehydration, in one pot. Under mild reaction conditions, a 63.2 % yield of PA is obtained from HMF. Compared with the currently reported route to renewable PA based on the Diels-Alder cycloaddition of biomass-derived MA and furan, this convenient one-pot synthesis represents a great improvement in efficiency.

Non-oxidative dehydrogenation of isobutane over supported vanadium oxide: nature of the active sites and coke formation

We combine Raman spectroscopy, EPR, XPS, temperature programmed reduction, XRD, ⁵¹V MAS ssNMR, TEM and N₂-physisorption to unravel structure–activity relationships during the non-oxidative dehydrogenation of isobutane over a V based catalyst.

Propane oxidative dehydrogenation over highly selective hexagonal boron nitride catalysts: The role of oxidative coupling of methyl

Hexagonal boron nitride (h-BN) catalyst has recently been reported to be highly selective in oxidative dehydrogenation of propane (ODHP) for olefin production. In addition to propene, ethylene also forms with much higher overall selectivities to C2-products than to C1-products. In this work, we report that the reaction pathways over the h-BN catalyst are different from the V-based catalysts in ODHP. Oxidative coupling reaction of methyl, an intermediate from the cleavage of C─C bond of propane, contributes to the high selectivities to C2-products, leading to more C2-products than C1-products over the h-BN catalyst. This work not only provides insight into the reaction mechanisms involved in ODHP over the boron-based catalysts but also sheds light on the selective oxidation of alkanes such as direct upgrading of methane via oxidative upgrading to ethylene or CH _x O _y on boron-based catalysts.

One-pot synthesis of vanadium-containing silica SBA-3 materials and their catalytic activity for propene oxidation

V-containing silica SBA-3 mesoporous catalysts were prepared by means of one-pot hydrothermal procedure with NH₄VO₃ or VOSO₄ as vanadium precursors under various acidic medium of the reaction mixture (pH < 1, 2.2 or 3.1). The combined spectral techniques (DR UV-vis, FTIR, EPR) as well H₂-TPR allowed to determine the nature of vanadium species in the studied samples. A successful incorporation of vanadium into the structure of silica SBA-3 was attained for the samples with low V content (<1 wt%), whereas the V-rich samples (i.e. >5 wt%) exhibited the presence of isolated vanadium and also of polynuclear surface species. The resulting V-bearing samples contain the Brønsted and Lewis acidic centres evidenced by FTIR spectra of adsorbed pyridine and by catalytic activity for 2-propanol decomposition and cumene cracking. Ammonia TPD allowed to estimate the number and strength of acid sites in regards to the vanadium content. Propene oxidation with N₂O revealed noticeable activity of the synthesised V-SBA-3 samples in epoxidation reaction. On the basis of TOF analysis indicating the activity of particular vanadium ions it seems that not all of the introduced V atoms take part in the formation of mild electrophilic oxygen species responsible for propene oxide formation.

Efficient SBA-3 vanadosilicate catalysts for propene oxidation obtained for the first time by the one-pot synthesis.

Structural characterization of vanadium environments in MCM-41 molecular sieve catalysts by solid state 51V NMR

Advanced analysis of ⁵¹V NMR chemical shift and quadrupolar tensor parameters revealed novel insights into the structure of vanadium species in MCM-41-based catalysts.

A TiO2/C catalyst having biomimetic channels and extremely low Pt loading for formaldehyde oxidation

This study presents a TiO₂/C hybrid material with biomimetic channels fabricated using a wood template. Repeated impregnations of pretreated wood chips in a Ti precursor were conducted, followed by calcination at 400–600 °C for 4 hours under a nitrogen atmosphere. The generated TiO₂ nanocrystals were homogenously distributed inside a porous carbon framework. With an extremely low Pt catalyst loading (0.04–0.1 wt%), the obtained porous catalyst could effectively oxidize formaldehyde to CO₂ and H₂O even under room temperature (conv. ∼100%). Wood acted as both a structural template and reduction agent for Pt catalyst generation in sintering. Therefore, no post H₂ reduction treatment for catalyst activation was required. The hierarchal channel structures, including 2–10 nm mesopores and 20 μm diameter channels, could be controlled by calcination temperature and atmosphere, which was confirmed by SEM and BET characterizations. Based on the abundant availability of wood templates and reduced cost for low Pt loading, this preparation method shows great potential for large-scale applications.

This study presents a TiO₂/C hybrid material with biomimetic channels fabricated using a wood template.

VRK, Y. W. S, P. S. SP, N. L. One-step selective synthesis of 2-chlorobenzonitrile from 2-chlorotoluene via ammoxidation

Isolated and polymeric vanadia formulate V₂O₅/Al₂O₃ catalysts selective for the synthesis of 2-chlorobenzonitrile from 2-chlorotoluene in a single step through ammoxidation.

Dispersed Vanadium in Three-Dimensional Dendritic Mesoporous Silica Nanospheres: Active and Stable Catalysts for the Oxidative Dehydrogenation of Propane in the Presence of CO2

The uniform monodispersed vanadium-doped three-dimensional dendritic mesoporous silica nanospheres (nV-MSNSs) were successfully synthesized in a heterogeneous oil-water biphase stratification reaction system and characterized by several state-of-the-art methods. The synthesized nV-MSNSs were applied to the oxidative dehydrogenation of the propane (ODHP) reaction with the presence of CO₂ and exhibited excellent catalytic performances. The results show that the vanadium loading (1.3-8.0 wt %) evidently influences the textural properties, oxidation state, and polymerization degree of vanadium species of nV-MSNSs. The specific surface area (S_BET), pore diameter (D_p), and pore volume (V_p) of nV-MSNSs decrease with the loading of vanadium species. The excessively high vanadium loading leads to the slight connection of nanospheres, but does not affect the assembly and growth of the three-dimensional (3D) dendritic channels. The percentage of highly dispersed vanadium V^V species gradually increases and attains the maximum value for 5.2V-MSNSs with the loading of vanadium and then decreases with further vanadium addition. The higher-polymerized VO_x species gradually generates above 5.2 wt % vanadium content for nV-MSNSs. The lower-polymerized VO_x species appear to be more active than the higher-polymerized VO_x species. Markedly, the 5.2V-MSNSs exhibit the highest catalytic activity with the initial propane conversion of 58% for the ODHP. The excellent catalytic performance can be maintained after eight reaction-regeneration cycles. The silica mesoporous frameworks can be well preserved in the reaction-regeneration cycles; meanwhile, the highly dispersed vanadium oxide also can be fully recovered after in situ regeneration. Hence, nV-MSNS catalysts exhibit outstanding activity and stability, and it would have a promising application in the DH of alkanes.

Synthesis and catalytic performance in the propene epoxidation of a vanadium catalyst supported on mesoporous silica obtained with the aid of sucrose

Sucrose is an effective template for mesoporous silica—an efficient support of vanadium catalysts, active in propene epoxidation to propylene oxide.

Electrocatalysis on copper–palladium alloys for amperometric formaldehyde sensing

A co-evaporated Cu–Pd thin film combinatorial library was screened for electrocatalytic oxidation of formaldehyde by scanning droplet cell microscopy. The best activity was found for 7.5 at% Pd and an amperometric sensor was fabricated and tested.

Synergy between vanadium and molybdenum in bimetallic ZSM-5 supported catalysts for ethylene ammoxidation

Ammoxidation of ethylene to acetonitrile was studied on V/ZSM-5, Mo/ZSM-5 and V–Mo/ZSM-5 catalysts prepared by a solid-state ion exchange method.

Catalytic activity of mesoporous Ni/CNT, Ni/SBA-15 and (Cu, Ca, Mg, Mn, Co)–Ni/SBA-15 catalysts for CO2 reforming of CH4

The CO₂ reforming of CH₄ to H₂ over a Ni/SBA-15 catalyst is an effective method for renewable energy generation.

Synthesis of sub-nanosized Pt particles on mesoporous SBA-15 material and its application to the CO oxidation reaction

In this work, we show that the size and shape of Pt nanoparticles in SBA-15 can be controlled through vacuum and air calcination. The vacuum-calcination/H2-reduction process is used to thermally treat a 0.2 wt% Pt(4+)/SBA-15 sample to obtain small 2D clusters and single atoms that can significantly increase Pt dispersion in SBA-15. Compared with thermal treatments involving air-calcination/H2-reduction, which result in ∼4.6 nm rod-like Pt particles, vacuum-calcination/H2-reduction can dramatically reduce the size of the Pt species to approximately 0.5-0.8 nm. The Pt particles undergoing air-calcination/H2-reduction have poor conversion efficiency because the fraction of terrace sites, the major sites for CO oxidation, on the rod-like Pt particles is small. In contrast, a large amount of low-coordinated Pt sites associated with 2D Pt species and single Pt atoms in SBA-15 is effectively generated through the vacuum-calcination/H2-reduction process, which may facilitate CO adsorption and induce strong reactivity toward CO oxidation. We investigated the effect of vacuum-calcination/H2-reduction on the formation of tiny 2D clusters and single atoms by characterizing the particles, elucidating the mechanism of formation, determining the active sites for CO oxidation and measuring the heat of CO adsorption.