Presence Of Lewis Acid Sites Research Articles

Phyllosilicate-derived Ni/SiO2 catalyst for liquid-phase hydrodeoxygenation of phenol: Synergy of Lewis acid sites and Ni0

Designing effective catalysts using non-noble metals for bio-oil hydrodeoxygenation (HDO) into liquid fuels is greatly sought after, yet it remains a great challenge. Contrary to the prevailing belief that monometallic nickel lacked activity in the HDO of oxygen-containing compounds, this study demonstrates a remarkable catalytic performance over monometallic Ni catalyst. Herein, a Ni/SiO2 catalyst having both nickel phyllosilicate and Ni0 was synthesized by the ammonia evaporation (AE) method. The Ni-PS-400 catalyst reduced at 400 ℃ achieves a significant high activity and yields 97 % cyclohexane at a low reaction temperature of 190 ℃, surpassing both Ni-IMP-400 prepared by impregnation method and most of the reported other non-noble metal catalysts which are generally used at high temperature of above 240 ℃. It was found that the reduction temperature of Ni-PS-X influences the catalytic activity, as more dispersed Ni nanoparticles and acidic sites can be produced on the surface of the support at an appropriate temperature. The outstanding catalytic performance can be ascribed to the collaborative effect of well-scattered Ni nanoparticles and the significant presence of Lewis acidic sites, which result from coordinatively unsaturated Ni2+ sites situated within the remaining nickel phyllosilicate.

Construction dual active sites on SnO2 via Fe doping for effective ciprofloxacin photodegradation

Adjusting the electronic structure via doping and enhancing the active sites of photocatalysts are proven strategies for improving the photodegradation of pollutants. However, the photodegradation mechanism involving doping elements and their impact on pollutant adsorption and activation at active sites remain unclear. In this study, Fe-doped SnO2 photocatalysts were synthesized using the hydrothermal method, featuring small particle sizes and highly active sites. It was found that doping SnO2 with 3 mol% Fe3+ significantly enhances its photocatalytic efficiency in degrading Ciprofloxacin, outperforming pure SnO2 by approximately 18.6 times. Spectroscopy methods, combined with density functional theory calculations, revealed that the presence of Lewis acid sites and oxygen vacancies serve as active sites in the Fe-doped SnO2 samples. Furthermore, a detailed photodegradation mechanism for Fe-doped SnO2 was proposed based on the band energy structure and analysis of free radical results. This research provides new insights into the mechanism of photocatalytic degradation of Ciprofloxacin by elucidating the interactions between the active sites of the photocatalyst and Ciprofloxacin molecules.

Valorisation of microalga Chlorella sp. into furans in the presence of Nb2O5 catalysts

Despite the interest in niobia-based catalysts and the importance of biomass valorisation, studies on these catalysts typically utilize model substrates like simple sugars. In this study, a series of niobium oxide-based catalysts was prepared for the application in aqueous phase catalytic conversion of sugars extracted from Chlorella sp. microalga into value-added furans. The solid catalysts were firstly characterized by various techniques including X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman and X-ray photoelectron (XPS) spectroscopy as well as low-temperature N2 physisorption. Moreover, the acidity of the catalysts was assessed by using the temperature-programmed NH3 desorption (NH3-TPD), by titration of water suspended catalyst with NaOH solution, and by P-bearing molecular probes loaded catalysts through 31P and 1H solid-state nuclear magnetic resonance (NMR) techniques. Herein, we focused on the catalytic transformation of Chlorella sp. and glucose solution as model molecule into furans. The best Nb2O5 catalysts for valorizing Chlorella sp. into furans exhibited a larger number of Brønsted acid sites, achieving conversion yields to 5-HMF and furfural of ca. 20–22 % with respect to the extracted sugars from algae. The results showed a discernible dependence of the conversion yields to 5-HMF and furfural on catalyst acidity, specific surface area, and the presence of the Brønsted acid sites. Conversely, when using the glucose solution as substrate is concerning, the highest yield to 5-HMF was reached by using a catalyst that showed also the presence of Lewis acid sites. A systematic investigation of the structure–activity relationships in niobium oxide application for aqueous phase dehydration using real biomass substrates to obtain furanic derivatives has not been documented thus far. Therefore, the current research is significant as it demonstrates the feasibility of transforming the carbohydrate content in microalgal biomass into furans by identifying the best catalyst to use.

Unleashing the potential of Boratrane and Silatrane: A game-changing approach for enhanced boron- and silicon- incorporation in phenol-formaldehyde resins and their thermal stability

In this study, we present an innovative and cost-effective method for the preparation of phenolic resin (PR) containing boron and silicon (BPR and BSiPR) using boratrane and silatrane. Through a one-pot synthesis via a sol-gel process, 3BPR and 3B5SiPR are successfully synthesized, utilizing boratrane and silatrane as the sources of boron and silicon. Our results demonstrate the effective introduction of boron and silicon elements into the PR matrix through the formation of BO4 (borate) and SiO4 (silicate) structures, as evidenced by Cph-O-B and B-O-Si linkages. Notably, the utilization of boratrane in the synthesis of 3BPR leads to the formation of a uniform structure of BO4, as confirmed by 11B-NMR analysis. Furthermore, the resulting resins exhibit an improved char yield of 72 % at 900 °C. The formation of borate and silicate species effectively reduces the content of phenolic hydroxyl groups, thus contributing to a decrease in weight loss during the carbonization process. Additionally, the migration of boron and silicon into the carbon structure promotes the formation of B4C and B8C crystal structures, resulting in the carbonization of resins and the formation of a graphene-like structure, as confirmed by Raman spectroscopy, which exhibits a broad 2D-band. The obtained carbon materials possess both Lewis acid and basic sites. The presence of Lewis acid sites was characterized through pyridine-adsorbed FTIR, while the Lewis basic sites and CO2 absorption were examined via TPD-CO2 analysis. The CO2 absorption capacities of 3BPR and 3B5SiPR were found to be 0.475 and 0.518 mmol/g, respectively.

Glycerol conversion in the presence of ethanol over CoFe2O4/SBA-15 mesoporous catalyst: Effect of the co-reagent on the catalytic performance

The synthesis and characterization of cobalt ferrite supported on mesoporous SBA-15 was presented to act as a catalyst in the glycerol conversion reaction in the presence of ethanol. Characterizations via X-ray diffraction (XRD) and FTIR spectroscopy confirmed the syntheses of SBA-15 and the CoFe2O4 phase dispersed on porous silica. Raman spectroscopy showed the ferrite with a degree of inversion (δ) of 0.4. The redox property was evaluated by TPR-H2 which exhibited reduction events above 400 °C, referring to the reduction of Co2+ and Fe3+ species. N2 physisorption analysis showed a surface area of 372 m2/g and a total pore volume of 0.65 cm3/g, indicating the presence of oxide on the surface and in the mesochannels of the support. Scanning electron microscopy (SEM) confirmed maintenance of support morphology after the impregnation process, while transmission electron microscopy (TEM) showed an average particle size of 6 nm for the supported cobalt ferrite. TEM images also confirmed that the typical mesoporosity of SBA-15 was maintained after spinel insertion. The acid-base properties of the catalyst indicated the presence of weak basic sites by CO2 temperature-programmed desorption (TPD-CO2) and the presence of Lewis acid sites by NO and Pyridine adsorption followed by FTIR analysis. The catalytic tests showed greater performance for the conversion glycerol in the presence of ethanol as co-reagent, considering that ethanol favors the interaction of glycerol with the solid surface and benefits the catalytic cycle. The reaction showed a conversion of only 20% in the absence of ethanol, while in the presence of the cosolvent a conversion greater than 80% was observed.

Indium exchanged heteropoly tungstates: Efficient catalysts for the synthesis of glycerol carbonate from glycerol and urea

In this study, heteropoly tungstate protons were exchanged with various amounts of indium to impart Lewis acidity in Keggin heteropoly acid catalysts. The synthesis of glycerol carbonate from urea and glycerol was investigated using the synthesized InxTPA catalysts. The prepared catalysts were characterized by Fourier transforms infrared (FTIR), X-ray diffraction (XRD), Laser Raman, and temperature programmed desorption of ammonia studies. The obtained characterization results confirmed that the existence of Keggin ion structure of heteropoly acid after modification with indium ions. The modification of heteropoly tungstate with transition metal ions was found to improve its acidity and the stability of heteropoly acids (HPAs). The presence of Lewis acidic sites associated with the indium ions present in the catalyst was indicated by pyridine adsorbed FT-IR spectra. The amount of indium ions in heteropoly tungstate had an impact on the catalysts acidity, which in turn affected the activity of catalyst. The partially exchanged In0.66TPA catalyst demonstrated 69.4% glycerol conversion with 98.8% selectivity to glycerol carbonate. The study also investigated the impact of various reaction parameters such as reaction time, mole ratio of glycerol to urea, reaction temperature, and catalyst concentration and established the optimum reaction conditions.

Understanding the cation exchange affinity in modified-MMT catalysts for the conversion of glucose to lactic acid.

This study investigated the exchange affinity of Fe3+, Cu2+, and Zn2+ cations in sulfuric acid-purified montmorillonite (S-MMT) to enhance Lewis acid sites and subsequently improve the catalytic conversion of glucose to lactic acid. XRD analysis suggested the successful cation exchange process, leading to structural expansion of the resultant cation exchanged-MMTs (CE-MMTs). XRF and TGA indicated that Zn2+ had the highest exchange affinity, followed by Cu2+ and then Fe3+. This finding was further supported by the results of TPD-NH3 analysis and pyridine-adsorption test, which demonstrated that Zn-MMT had the highest total acid sites (TAS) and the ratio of Lewis acid-to-Brønsted acid surface site (LA/BA). These results indicated dominant presence of Lewis acid sites in Zn-MMT due to the higher amount of exchanged Zn2+ cations. Consistently, time-dependent catalytic studies conducted at 170 °C showed that a 7 h-reaction generated the highest lactic acid yield, with the catalytic performance increasing in the order of Fe-MMT < Cu-MMT < Zn-MMT. The study also observed the impact of adding alcohols as co-solvents with water at various ratios on the conversion of glucose to lactic acid catalysed by Zn-MMT. The addition of ethanol enhanced lactic acid yield, while methanol and propanol inhibited lactic acid formation. Notably, a water-to-ethanol ratio of 30 : 70 v/v% emerged as the optimal solvent condition, resulting in ca. 35 wt% higher lactic acid yield compared to using water alone. Overall, this study provides valuable insights into the cation exchange affinity of different cations in MMT catalysts and their relevance to the conversion of glucose to lactic acid. Furthermore, the incorporation of alcohol co-solvent presents a promising way of enhancing the catalytic activity of CE-MMTs.

Synthesis, Characterization and Photocatalytic Activity of CoFe2O4/Fe2O3 Dispersed in Mesoporous KIT-6.

The present work aimed to synthesize and characterize a solid based on CoFe2O4/Fe2O3-KIT-6 and evaluate its performance in the photocatalytic degradation of the remazol red ultra RGB dye. By analyzing XRD, N2 physisorption, and Mössbauer results, it was possible to identify that the desired CoFe2O4/Fe2O3 phase was achieved, which maintained its structural properties. The FTIR-pyridine indicated the presence of Lewis acid sites, while TPD-CO2 showed a large amount of weak basic sites. The band-gap energy indicated that the compound can be applied in photocatalytic degradation under UV/visible light, with the possibility of magnetic separation at the end of the reaction. The photocatalysis results indicated that there was complete degradation of the remazol red ultra RGB dye within 1 h of reaction. Despite the absence of H2O2, the combination of the proposed photocatalyst with the anatase phase (TiO2) showed significant improvements in the degradation process. The proposed mechanism for complete dye degradation indicated that a sequence of radical reactions is necessary, generating oxidant species such as •OH and the final products were CO2 and H2O.

Alkali metal ion assisted preparation of zeolite encapsulated small cobalt cluster CoOx for direct styrene oxidation to benzaldehyde

Zeolites with metal clusters encapsulated within the pore structure have attracted more attention because of their unique properties with high stability, but diffusion resistance is the bottleneck limiting the utilization efficiency of active centers, especially in macromolecular reactions. Hollow zeolites could effectively improve mass transport by reducing the wall thickness. In this work, cobalt-base hollow silicate-1 zeolite was obtained by mother liquid treatment with sodium chloride. Various characterization results show that the CoOx@HS-1-0.5Na+ crystals have completely hollow structure and small cobalt cluster highly dispersed encapsulated in it. The presence of Lewis acid sites and the unique hollow structure resulted in enhanced selectivity to benzaldehyde in the styrene oxidation. The effect of various factors including cobalt loading, the concentration of sodium ion, reaction solvents and H2O2/styrene molar ratio on the catalytic performance were systematically investigated. The yield of benzaldehyde can achieve 73.8% with 83.59% styrene conversion and 88.29% benzaldehyde selectivity.

Solvent-free synthesis of a zirconium-carbon coordination catalyst for efficient aqueous-phase production of lactic acid from xylose

It is highly desirable but of challenge to develop an efficient process for lactic acid (LaA) production from xylose performed in water. Herein, a novel catalyst prepared via a facile solvent-free coordination route is developed to efficiently produce LaA from xylose in water. The structural properties of the prepared catalyst and the reaction conditions are systematically investigated. The production rate of LaA at 190 °C in water is up to 1.8 h−1, outperforming the most recent reports (below 1.1 h−1). Detailed experimental and characteristic studies reveal that the presence of Lewis acidic sites and basic sites in the catalyst structure can not only lower the energy barrier of xylose conversion but also boost the efficient conversion of the active reaction intermediates into LaA. The findings of this work will provide a new approach for the efficient production of LaA from carbohydrates.

Perlite Supported Cobalt Oxide Catalyst for a Series of Liquid‐Phase Esterification Reactions

AbstractThermally activated perlite‐supported cobalt oxide (Co‐TAP) catalyst has been synthesized via the deposition‐precipitation method. FTIR peaks at around 663 and 565 cm–1 and XRD peaks arise from diffraction of FCC planes of CoO crystals confirm the presence of Co3O4 crystallites on Co‐TAP surface. UV–Vis DRS studies reveal the presence of octahedrally coordinated Co3+ and tetrahedrally coordinated Co2+ ions. EDX analysis of Co‐TAP clearly shows the enhanced percentage of silica and cobalt oxide. All characterization studies suggest the presence of Lewis acidic sites on Co‐TAP which have been utilized in a series of liquid‐phase esterification reactions of benzoic acid with various alcohols over three different reaction media (conventional, microwave, and sonication). The reactions are carried out in one‐pot, single‐step, solvent‐free reaction conditions, and the catalyst is filtered easily, regenerated, and reused up to five reaction cycles with analogous efficiency suggesting that acidic sites of the catalyst remain stable in all reaction mediums. The stability of regenerated Co‐TAP catalyst after the fifth reaction cycle is confirmed by FTIR spectrum which resembles the FTIR of fresh catalyst.

Al2O3 nanofibers prepared from aluminum Di(sec-butoxide)acetoacetic ester chelate exhibits high surface area and acidity

Alumina (Al2O3) is a widely used material for catalysis in the chemical industry. Besides a high specific surface area, acid sites on Al2O3 play a crucial role in the chemical transformation of adsorbed molecules, which ultimately react and desorb from the catalyst. This study introduces a synthetic method based on electrospinning to produce Al2O3 nanofibers (ANFs) with acidity and porosity tuned using different aluminum precursor formulations. After electrospinning and heat treatment, the nanofibers form a non-woven network with macropores (∼4 μm). Nanofibers produced from aluminum di(sec-butoxide)acetoacetic ester chelate (ASB) show the highest total acidity of ca. 0.70 µmol/m2 determined with temperature-programmed desorption of ammonia (NH3-TPD) and BET. The nature of the acid site in ASB ANFs is studied in detail with infrared (IR) spectroscopy. Pyridine is used as a molecular probe for the identification of acid sites in ASB. Pyridine showed the presence of Lewis acid sites prominently. Density-functional theory (DFT) is conducted to understand the desorption kinetics of the adsorbed chemical species, such as ammonia (NH3) on crystalline γ-Al2O3. For our analysis, we focused on a mobile approach for chemisorbed and physisorbed NH3. The computational results are compared with NH3-TPD experiments, ultimately utilized to estimate the desorption energy and kinetic desorption parameters. The experiments are found to pair up with our simulation results. We predict that these non-woven structures will find application as a dispersion medium of metallic particles in catalysis.

Lewis Acid Strength of Interfacial Metal Sites Drives CH3OH Selectivity and Formation Rates on Cu‐Based CO2 Hydrogenation Catalysts

AbstractCH3OH formation rates in CO2 hydrogenation on Cu‐based catalysts sensitively depend on the nature of the support and the presence of promoters. In this context, Cu nanoparticles supported on tailored supports (highly dispersed M on SiO2; M=Ti, Zr, Hf, Nb, Ta) were prepared via surface organometallic chemistry, and their catalytic performance was systematically investigated for CO2 hydrogenation to CH3OH. The presence of Lewis acid sites enhances CH3OH formation rate, likely originating from stabilization of formate and methoxy surface intermediates at the periphery of Cu nanoparticles, as evidenced by metrics of Lewis acid strength and detection of surface intermediates. The stabilization of surface intermediates depends on the strength of Lewis acid M sites, described by pyridine adsorption enthalpies and 13C chemical shifts of ‐OCH3 coordinated to M; these chemical shifts are demonstrated here to be a molecular descriptor for Lewis acid strength and reactivity in CO2 hydrogenation.

Lewis Acid Strength of Interfacial Metal Sites Drives CH3 OH Selectivity and Formation Rates on Cu-Based CO2 Hydrogenation Catalysts.

CH3 OH formation rates in CO2 hydrogenation on Cu-based catalysts sensitively depend on the nature of the support and the presence of promoters. In this context, Cu nanoparticles supported on tailored supports (highly dispersed M on SiO2 ; M=Ti, Zr, Hf, Nb, Ta) were prepared via surface organometallic chemistry, and their catalytic performance was systematically investigated for CO2 hydrogenation to CH3 OH. The presence of Lewis acid sites enhances CH3 OH formation rate, likely originating from stabilization of formate and methoxy surface intermediates at the periphery of Cu nanoparticles, as evidenced by metrics of Lewis acid strength and detection of surface intermediates. The stabilization of surface intermediates depends on the strength of Lewis acid M sites, described by pyridine adsorption enthalpies and 13 C chemical shifts of -OCH3 coordinated to M; these chemical shifts are demonstrated here to be a molecular descriptor for Lewis acid strength and reactivity in CO2 hydrogenation.

Magnesium Hydrogen Phosphate: An Efficient Catalyst for Acrylic Acid Production from Biorenewable Lactic Acid.

A series of Magnesium hydrogen phosphate (MgHP) catalysts with different magnesium to phosphorous (Mg/P) mole ratios at varying calcination temperatures has been synthesised, bearing in mind the effectiveness as well as the stability of MgHP to catalyse acrylic acid (AA) production from biorenewable lactic acid (LA), a synthetic process applicable to biomass conversion. The physicochemical properties of the MgHP catalysts have been thoroughly characterised and the formation of Mg(NH₄)PO₄, MgHPO₄ and Mg₂P₂O7 with different structural and acidic properties have been reported. The high catalytic performance of MgHP catalysts with high AA yields (100% conversion and 85% selectivity) at high space velocities (WHSVLA = 3.13 h-1) have been achieved at 360 °C. NH₃-Temperature programmed desorption (TPD) and pyridine FTIR have shown that the effectiveness of a catalyst is accounted for not primarily by the actual strength of acidic sites, but is due to the presence of Lewis acidic sites compared to Bronsted sites.

Mesoporous KIT-6 supported Cr and Co-based catalysts for microwave-assisted non-oxidative ethane dehydrogenation

Abstract In the present study, mono and bi-metallic catalysts containing Cr and Co were prepared by impregnating the hydrothermally prepared mesoporous KIT-6 support with 5–10 wt% total metal content. The well-ordered three-dimensional mesoporous structure of the KIT-6 support was confirmed by small angle X-ray diffraction (XRD) patterns. N2 adsorption-desorption analysis results showed that the mesoporous structure of KIT-6 was preserved after metal loading. Structural bonds of KIT-6 support and prepared catalysts were determined by Fourier-transform infrared (FT-IR) spectroscopy. The pyridine adsorbed diffuse reflectance FT-IR (DRIFT) spectroscopy results revealed the presence of Lewis acid sites on the surface of the catalysts. Activity experiments were carried out in a microwave-heated continuous-flow fixed bed reactor system at temperature range of 350–650 °C and feed ratios of Ethane/Argon: 1/2, 1/1, 2/1 with a gas hourly space velocity (GHSV) of 18,000 ml/h.gcat. The 5Cr@KIT-6 catalyst exhibited high ethane conversion (63.5%) while the highest ethylene/hydrogen ratio (0.98) was obtained with the 2.5Cr2.5Co@KIT-6 catalyst at 450 °C. It was concluded that high temperatures (above 450 °C) facilitate the formation of side reactions and the production of aromatic compounds. The high catalytic activities of mesoporous catalysts were thought to be due to hot spots in the microwave reactor system.

Investigation of the effect of microwave heated reactor on ethane dehydrogenation over KIT-6 supported catalysts

Non-oxidative conversion of ethane to hydrogen and ethylene was carried out with Cr and Co-based KIT-6 supported catalysts in a conventional heated reactor (C-HRS) and microwave heated reactor (M-HRS) systems. The catalysts were synthesized by wet impregnation of hydrothermally prepared KIT-6 support. X-ray diffraction (XRD) and N2 adsorption–desorption studies showed that the well-ordered three-dimensional mesoporous structure of the KIT-6 support was preserved after 10wt% metal loading. The pyridine adsorbed diffuse reflectance FT-IR (DRIFT) spectroscopy results revealed the presence of Lewis acid sites on the catalysts. The incorporation of Co into the structure slightly increased the Lewis acid sites. The Cr@KIT-6 catalyst exhibited the highest ethylene and hydrogen selectivity with a C2H4/H2 ratio of 1.00 at 650 °C in C-HRS. To compare the effect of active metal on the catalytic activity, Co@KIT-6 catalyst was tested at 650 °C in C-HRS. Although, the ethane conversion values of Cr and Co-based catalysts were similar, Co@KIT-6 catalyst exhibited lower C2H4/H2 ratio (0.51). The characterization studies of the spent catalysts confirmed higher amount of coke deposited on the Co@KIT-6 catalyst. The effect of microwave-assisted heating on the catalytic activity was investigated with Cr and Co-based catalysts at 450 °C in M-HRS. It was determined that much higher ethane conversion and yield values were obtained even at lower temperatures in M-HRS compared to the C-HRS. While the H2 yield was 0.15 at 650 °C in C-HRS, this value increased to 0.37 at 450 °C in M-HRS.

Propylene and aromatics from ethylene conversion over ZSM-5: Effect of zeolite composition

Bioethanol is a green alternative to supply the demand for light olefins (ethylene and propylene) and aromatics (benzene, toluene, and xylenes) that can have a green label. ZSM-5 zeolite is largely used to produce light olefins and aromatics from ethanol or ethylene. The addition of metal species to ZSM-5 can tune the activity and selectivity of the zeolite to specific compounds. The influence of the incorporation of tungsten, iron, and lanthanum species on ZSM-5 was studied. The presence of tungsten species favored the formation of aromatics, while lanthanum promoted the production of light olefins. The density of acid sites and the presence of sites with intermediate strength influenced the ethylene conversion and the product distribution of the metal impregnated zeolites. Moreover, the presence of Lewis acid sites promoted the production of aromatics. However, the role played by the acid properties is dependent on the experimental conditions employed. The reaction routes were elucidated, that is, the aromatics are mainly formed through dehydrocyclization on WHZSM-5, while the olefins are produced from the reaction of ethylene and carbene species (propylene) and the dimerization of ethylene (butenes) on LaHZSM-5.

Catalytic hydrogenation of nitrate in water: improvement of the activity and selectivity to N2 by using Rh(III)-hexamolybdate supported on ZrO2–Al2O3

ABSTRACT Catalysts prepared on ZrO2, Al2O3 and ZrO2–Al2O3 (ZrAl-10) supported with Anderson heteropolyanion (RhMo6) as active phase were investigated for the elimination of NO3 − from water. Raman characterization of pure and supported RhMo6 phase showed the presence of polymolybdic species of different degrees of complexity when RhMo6 was supported. The temperature-programmed reduction study revealed the synergic effect between Rh and Mo species, through which the reducibility of Mo was promoted by Rh, and different phase/support interactions were verified. Among the supports, ZrAl-10 presented the highest acidity due to the presence of ZrO2 in the tetragonal modification and high specific surface area (due to Al2O3), favouring rhodium–molybdenum active phase/support interaction and high dispersion. All catalysts prepared were active in removing NO3 −, the one prepared with the RhMo6 phase on the ZrAl-10 support being the most active. These results point to the formation of an active surface with a high dispersion of Rh and Mo. The highest selectivity to N2 (99.3) exhibited by the RhMo6/ZrAl-10 catalyst is proposed to be related to the high Rh dispersion (0.755) and to the presence of Lewis acid sites (oxygen vacancies) of the tetragonal ZrO2 modification that favour NO3 − adsorption through electrostatic interactions.

Direct aerobic oxidation of monoalcohol and diols to acetals using tandem Ru@MOF catalysts

The aerobic oxidation of monoalcohols and diols to acetals is an important academic and industrial challenge for the production of fine chemicals and intermediates. The existing methods usually rely on a two-step process in which alcohols are first oxidized to aldehydes over metal catalysts (Ru, Pt, Pd) and then acetalized using acids. Due to the instability of aldehydes, how to avoid over-oxidation to their respective carboxylic acids and esters is a long-standing challenge. For this reason, certain non-conjugated dialdehydes have never been successfully produced from diol oxidation. Hereby we report a Ru@metal-organic framework (MOF) tandem catalyst containing ultra-fine Ru nanoparticles (< 2 nm) for direct alcohol to acetal conversion of monoalcohol and diols with no formation of carboxylic acids. Mechanistic study reveals that the presence of Lewis acid sites in the MOF work in concert with Ru active sites to promptly convert aldehydes to acetals thereby effectively suppressing the formation of over-oxidation byproducts.