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Catalytic conversion of CO2 to valuable products is a promising way to reduce anthropogenic CO2 emission. Herein, a strategy for coupling conversion of CO2 and high‐carbon alkane to CO and gasoline is developed, which is a feasible choice for the combination of CO2 recycling and petroleum refining. The CO2 conversion reaches 2.6% under mild condition (270 °C), and the selectivity of gasoline in the cracking products exceeds 70 wt%. Additionally, the introduction of CO2 improves the selectivity of aromatic hydrocarbons and increases the octane number of gasoline. Mechanism studies indicate that synergistic effect between Brønsted acid centers and Ni sites on the Beta zeolite supported Ni (20 wt%) catalyst (20Ni/β) plays the key role in alkane cracking and CO2 reduction. Notably, 13CO2 isotopic experiments show that the hydrogen produced during the aromatization can be captured by CO2, inhibiting undesired hydrogen transfer pathways and enhanced the yield of aromatics, while CO2 is converted into valuable CO. [ABSTRACT FROM AUTHOR]

We carried out a mechanistic investigation of the dehydration of fructose catalyzed by a series of proton‐exchanged faujasite zeolites. Using a combination of analytical tools (HPLC, GC, NMR), we could solve and quantify most of the variety of products formed, including (i) cyclic intermediates (ii) transient species (monomeric and dimeric) (iii) byproducts (oligomeric species and humins). The results prove that the reaction goes through a cyclic mechanism, and we could propose a kinetic model matching most of our experimental results and describing the interplay between the different categories of products. By comparing the performances of different catalysts with varying properties, we surprisingly find that increasing the concentration of Brønsted acid sites induces lower catalytic activity. Contrary to general expectations, the mesoporous volume seems to be the most determining parameter for the activity of the catalysts over the set of catalysts evaluated here, which may be explained by the importance of allowing the reactant a significant accessibility to the active sites. [ABSTRACT FROM AUTHOR]

Ketonization of biomass‐derived carboxylic acids offers a promising approach to remove oxygen and upgrade into valuable chemicals. However, the mechanism on Brønsted acid site (BAS) confined in micropores of zeolite remains elusive, due to the difficulty to observe the reaction intermediates experimentally and to locate the transition state via static density functional theory (DFT) calculations. Herein, ketonization of acetic acid on HBEA at 673 K was studied by metadynamics simulations based on DFT. The first reaction step was the concerted protonation and dehydroxylation of acetic acid, resulting in an electrophilic acylium cation and H2O (ΔG‡ = 1.53 eV). The subsequent likely steps, including C─C coupling through the nucleophilic attack of acetic acid (path I), ketene (path II), and 1,1‐dihydroxyethene (path III) toward acylium cation were tracked and compared. The high barriers for formation of more nucleophilic intermediates of ketene and 1,1‐dihydroxyethene made the overall path II and III less favorable than the direct coupling between acetic acid and acylium cation (path I, ΔG‡ = 2.15 eV). These results indicate that acylium cation is a key intermediate, and the C─C coupling between acetic acid and acylium cation via nucleophilic attack is the most favorable path on BAS confined in zeolite. [ABSTRACT FROM AUTHOR]

Catalyst‐controlled diversity‐oriented synthesis (CatDOS) is an important research area for expanding molecular complexities and achieving high atomic economics. Many regiodivergent syntheses have been achieved through metal catalysis, covalent organocatalysis, and non‐covalent organocatalysis by controlling the molecular recognition function of the catalysts. However, the development of regiodivergent CatDOS through Brønsted base organocatalysis was relatively less developed than others so far. Numerous studies about Brønsted base organocatalysis have demonstrated the powerful molecular recognition abilities of their cationic conjugate acids mainly in controlling the stereoselectivity instead of the regioselectivity. This concept review aims to conceptualize a new perspective to consider the potential role of the cationic conjugate acid of Brønsted bases for regiodivergent CatDOS. Recent representative examples are selected to demonstrate the potential of cationic conjugate acids in site‐selectivity control in single bond and multiple bonds formation reactions. The summarized results show that even the conjugate acid of common tertiary amines, protic ammonium ions, could affect the regioselectivity in the early‐ or late‐stage step during multiple bonds formation after initial deprotonation. The results also suggested that the properties and ion‐pairing interactions of conjugate acid could be more important than the basicity of the base in controlling regioselectivity. Perspectives and hypotheses for explaining the mechanism of regioselectivity are also included in this review. [ABSTRACT FROM AUTHOR]

The different structural‐type zeolites (FER, MFI, FAU, BEA) are investigated as catalysts in (bio)isobutanol conversion into linear butenes. The zeolites' structure and morphology are confirmed by XRD, N2 (77 K) ad(de)sorption, SEM, EDX, XPS, and 27Al, 29Si, 1H MAS NMR, 1H‐29Si CP MAS NMR. The nature and strength of acid‐base sites are determined by FTIR spectroscopy of adsorbed pyridine, potentiometric titration, and TPD of NH3/CO2/H2O with MS control. The acid‐base properties of the zeolites′ surfaces influence their catalytic properties in the target process. The higher selectivity towards linear butene isomers achieved over FER and MFI can be explained by the high strength and density of Brønsted acid sites (over 90 % of the total surface acidity). MFI might be regarded as a potential material for the creation of novel catalysts for isobutanol conversion into linear butenes at moderate temperatures (448–473 K) since it offers greater operating stability throughout the process. [ABSTRACT FROM AUTHOR]

The experimentally obtained kinetic data has indicated the existence of a synergetic cocatalytic effect provided by an iodonium salt in the base‐catalyzed Knoevenagel condensation. The diphenyliodonium triflate serving as the halogen bond‐donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving, respectively, as the metal cation‐based Lewis acid and Brønsted acid. Such a cocatalytic effect remains the same for a broad scope of carbonyl compounds covering aldehydes featuring electron‐withdrawing or electron‐donating substituents, as well as ketone involved in the reaction. [ABSTRACT FROM AUTHOR]

The role of Lewis and Brønsted acid sites in the Diels‐Alder cycloaddition (DAC) of ethylene to 2,5‐dimethylfuran (2,5‐DMF) to p‐xylene was investigated. Amorphous silica catalysts containing Al3+ (ASA), Ga3+ (ASG), and In3+ (ASI) were prepared via homogeneous deposition‐precipitation. Silica modified with Zr4+ (ASZ) was prepared by impregnation. Their acidic properties were characterized by various IR and NMR spectroscopic techniques. Measurements using pyridine as a probe molecule highlighted the presence of mostly Lewis acid sites (LAS) in all materials. Using CO as a probe, in contrast, demonstrated the existence of Brønsted acid sites (BAS) in ASA and ASG, which were nearly absent in ASI and ASZ. Differences in basic strength can explain the contrast in results observed between the two probe molecules. The highest p‐xylene yield (~20 %) in the DAC reaction, could be achieved with ASA and ASG. The lack of BAS in ASI and ASZ resulted in inferior performance in the DAC, with p‐xylene yields below 5 %. These results indicate the importance of BAS for the DAC reaction. Several other heterogeneous and homogeneous catalysts were explored for the DAC reaction to show the generality of our conclusion that BAS play a critical role in obtaining p‐xylene from 2,5‐DMF and ethylene. [ABSTRACT FROM AUTHOR]

Herein, desilication in increasingly harsh conditions was used to introduce mesopores into two different industrial ZSM‐5 catalysts (Si/Al ratio 11 or 29). For desilicated samples, increasing BET surface areas, mesopore volumes, and Si(OH) densities were noted. Brønsted acid site (BAS) densities increased upon desilication, as formerly inaccessible BAS in blocked pores became available, while the strength of the BAS was maintained upon desilication. Using KOH instead of NaOH as desilication agent can increase the mesopore volume generated per mass loss. The correlations between desilication strength and properties were largely determined by the parent Si/Al ratio. In general the introduced mesopores increased lifetimes in the ETA conversion, while additional Si(OH) groups introduced by desilication reduce the lifetime again. The lifetime is thus determined by a complex interplay of BAS density, improved reactant transport by introduced mesopores and Si(OH) density. There were no additional aromatics formed in desilicated samples during the conversion of ethanol and the samples were, in terms of aromatic yield, outperformed by a microporous parent. However, as result of longer lifetimes less ethanol was lost due to coke formation. It is concluded that desilication should be combined with other post‐modifications to increase aromatic production and lifetime. [ABSTRACT FROM AUTHOR]

Levulinic acid and angelica lactones are important building blocks obtained from hemicellulose. This process comprises multiple chemical reactions at which furfuryl alcohol is an intermediate, but only few studies have investigated its hydrolysis. This work studied the role played by the nature of acid sites and the impact of their strength and amount on furfuryl alcohol hydrolysis over Nb2O5 and NbOPO4. It was disclosed that production of levulinic acid is a two‐step cascade reaction at which angelica lactones are intermediates. These two hydrolysis steps were catalyzed by Brønsted acid sites with no contribution from Lewis centers. Brønsted acidity of Nb2O5 presented no activity while phosphate moieties on NbOPO4 were effective. Mixtures of organic solvent and water hindered side reactions, improving selectivity to valued bioproducts. 1,4‐dioxane was the most suitable organic solvent. This study shows that selectivity of 96 % of levulinic acid and angelica lactones can be accomplished over NbOPO4. [ABSTRACT FROM AUTHOR]

Mesoporous ZSM‐5 catalysts were prepared from a commercial ZSM‐5 (Si/Al=15), using a 2‐step micelle‐templating procedure. By varying the NaOH/Si synthesis ratio in the range of 0.3‐0.7, ZSM‐5 catalysts with different textural and acidic properties were obtained. Increasing the NaOH/Si ratio in the synthesis gel leads to zeolites that feature reduced number of Brønsted acid sites, but higher mesopore volume, which allows for reducing the diffusion path length. In order to assess the best compromise between Brønsted acidity and mesopore volume two test reactions were run. The alkylation of phenol with tert‐butyl alcohol allowed to evidence the accessibility of bulky molecules to active sites. The esterification of benzyl alcohol with hexanoic acid allowed to probe the specificity of Brønsted acid sites in ZSM‐5. The best compromise was found for micro‐/mesoporous ZSM‐5 catalysts prepared with the ratio 0.38

Based upon their exceptional reactivity as cooperative Brønsted acid‐base catalysts chiral diphosphane Pd‐aqua complexes have successfully been utilized in a broad range of asymmetric transformations. Originally discovered by Sodeoka 25 years ago, they readily form reactive chiral Pd enolates upon deprotonation of β‐dicarbonyl compounds and simultaneously, a Brønsted acid liberated from the catalyst activates the electrophile. After the initial report and some ensuing papers had been published in the early 2000s, the field lay dormant for more than a decade. In recent years, however, new developments towards the enantioselective synthesis of various heterocycles and other useful compounds have evolved which take advantage of the unique properties of chiral Pd‐aqua complexes. [ABSTRACT FROM AUTHOR]

Zirconium (Zr) was doped to optimize the NH3‐SCR activity of both CeO2 and thiourea modified CeO2‐TA catalysts for comparison. Different from the promotional influence of thiourea modification on the agglomeration of CeO2, the transformation from nanoparticles to nanocubes and the formation of highly crystallized CeOSO4, Zr doping lowers the agglomeration of nanoparticles, loosens the surface morphology of catalyst and promotes the formation of Ce‐Zr solid solution. Furthermore, Zr doping exhibits a synergistic promotional effect of thiourea modification on the dispersion of Ce3+ and S6+ species on the surface of CeO2, and increases the concentrations of the surface total oxygen and chemisorbed oxygen of CeO2‐TA. Interestingly, Zr doping instead decreases the promotional effect of thiourea modification on the high‐temperature or medium/low‐temperature reducibility of catalyst, but increases both Brønsted and Lewis acid sites of CeO2‐TA by inducing the highly dispersive sulfate species rather than the CeOSO4 crystal, which might be crucial to the NH3‐SCR activity of Ce‐based catalyst. [ABSTRACT FROM AUTHOR]

Faujasite is one of the most industrially employed zeolite for its catalytic properties. The strong Brønsted bulk bridging Al−OH−Si sites are often thought to be the main origin of the Brønsted acidity of faujasite. However, many reactions also take place at the surface of the material and of its mesopores, where other types of acid sites exist. This study aims at unraveling the nature and strength of faujasite bulk and surface acid sites. Using Density Functional Theory (DFT), we rank the faujasite acid sites based on their stability, investigate their dehydration properties, and study their Brønsted and Lewis acidity via the adsorption of pyridine. Calculations are performed on cells with high (47 for bulk cells and about 300 for surface slabs) and low Si/Al ratio (about 3) and on cells containing defects under the form of silanol nests. These environments generate Brønsted acid sites of various strengths, and strong Lewis acid sites, even in the absence of extra‐framework species. [ABSTRACT FROM AUTHOR]

γ‐Valerolactone (GVL) is a renewable and versatile platform chemical derived from sustainable carbon feedstocks. The cascade conversion of levulinic acid into GVL requires Brønsted and Lewis acid catalysed reactions. Here, a dual‐catalyst bed configuration is demonstrated that promotes synergy between Brønsted acid sites in sulfated zirconia (SZ) and Lewis acid sites in ZrO2/SBA‐15 for the liquid phase, continuous flow esterification and subsequent catalytic transfer hydrogenation (CTH) of levulinic acid to GVL. A saturated surface sulfate monolayer, possessing a high density of strong Brønsted acid sites, was optimal for levulinic acid esterification to isopropyl levulinate over SZ (>80 % conversion). A conformal ZrO2 bilayer, deposited over a SBA‐15 mesoporous silica and possessing mixed Brønsted:Lewis acidity, catalysed CTH of the levulinate ester and subsequent dealcoholisation/cyclisation to GVL (>60 % selectivity). Maximum stable productivity for the dual‐bed was 2.2 mmolGVL.gcat.h−1 at 150 °C, significantly outperforming either catalyst alone or a physical mixture of both. Flow chemistry is a versatile approach to achieve spatial control over cascade transformations involving distinct catalytically active sites. [ABSTRACT FROM AUTHOR]

This review discusses the immense progress made over recent years in metal‐free catalytic hydroboration. Reactions with several unsaturated functional groups, such as alkynes, alkenes, carbonyl compounds, carbon dioxide, carbodiimides, imines, allenes, pyridines, carboxylic acid derivatives etc., have been explored. Although there are significant developments in hydroboration reactions using metal‐based catalysts, metal‐free catalytic strategies are more desirable from a sustainability perspective. Considerable effort has been made by various research groups on metal‐free catalysts in the hydroboration of unsaturated compounds. Lewis acid, Brønsted acid, Lewis acid‐base pairs, and frustrated Lewis pairs were involved as metal‐free sources to catalyze hydroboration reactions in a sustainable manner. Detailed mechanisms of the catalytic pathways of metal‐free hydroboration are also discussed in this review. This discussion will provide an overview of the extent of work carried out as well as indicate scope for future research. [ABSTRACT FROM AUTHOR]

Alkynes are one of the most abundant feedstocks for chemical transformations. By merging palladium and Brønsted acid catalysts, they are converted into reactive allylmetal species, which become suitable for Tsuji‐Trost functionalizations with complete atom‐economy. This approach, which overcomes the limitations of traditional methods that suffer from the formation of over‐stoichiometric amounts of by‐products, has been disclosed for developing new C−C and C−Het bond forming methodologies. Within this review, we aim to survey the latest advancements in this area including applications in polymer chemistry, deuterium‐labeling and stereoselective catalysis. [ABSTRACT FROM AUTHOR]

For Pt‐WOx‐based catalysts, researchers pay much attention to study the influence of Pt‐WOx interaction on glycerol hydrogenolysis, ignoring the interaction between WOx and support. Herein, four Pt/W/SiZr‐T catalysts with different surface hydroxyl groups on support are prepared and characterized. The results show that bibridged (OHII) and tribridged hydroxyl groups (OHIII) on SiZr‐T supports could react with WOx species through forming Zr−O−W bands and retard the agglomeration of WOx species. The highly dispersed WOx species and Zr−O−W bands are the origination of inherent and in‐situ generated Brønsted acid, which are beneficial for 1,3‐propanediol synthesis. As a result, Pt/W/SiZr‐70 exhibits outstanding performance due to abundant OHII and OHIII on SiZr‐70. The initial space time yield of 1,3‐propanediol on Pt/W/SiZr‐70 reaches 2.280 g1,3‐PDO ⋅ gcat−1 ⋅ h−1, the highest among reported results. This r esearch reveals the role of WOx‐support interaction on glycerol hydrogenolysis and provides a new direction to design Pt‐WOx‐based catalysts for selective hydrogenation reactions. [ABSTRACT FROM AUTHOR]

The potential of amorphous silica‐alumina (ASA) to substitute zeolites (HBeta‐25) for the synthesis of p‐xylene via Diels‐Alder cycloaddition (DAC) of ethylene to 2,5‐dimethylfuran (2,5‐DMF) is investigated. ASA were prepared via homogeneous deposition‐precipitation of Al on SiO2. ASA shows good yields of p‐xylene (20–25 % after 18 hours) compared to bare silica and γ‐alumina. Brønsted acid sites (BAS) were identified as the active sites for the DAC reaction. The catalytic performance correlated strongly with the BAS concentration. Increasing the acidity of ASA is, however, limited by formation of agglomerated alumina‐type clusters at higher Al3+ content. While HBeta‐25 zeolite shows initially a slightly higher performance in terms of p‐xylene yield, ASA is the better catalyst upon calcination‐regeneration of the used catalyst. These results furthermore confirm that confinement in zeolite micropores is not a prerequisite for the DAC reaction between 2,5‐DMF and ethylene. [ABSTRACT FROM AUTHOR]

The interface and surface acidity of heterogeneous catalysts are widely applied to manipulate the catalytic performance. However, the interface structure prepared by traditional synthesis processes required multistep procedures, which was still lack of controllability and stability. Here, we show a general synthetic approach to fabricate ultra‐stable heterogeneous catalysts with tailored molecular interfacial structure and super acidity in one step. The as‐synthesized SiW12Ox/TiO2 catalyst was used for photo‐catalytic conversion of methane to value‐added oxygenates. We propose that the formed molecular interface W12−OH−Ti coupled with the introduced Brønsted acid sites of POMs, results in enhancing the photocatalytic performance. Namely, the addition of SiW12Ox can reduce the recombination of electrons and holes for triggering charge separation owing to the photoelectron capturing by proton, improving electron transfer to reactants and thereby promoting catalytic activity. This fabrication method provides a way to build molecular interface photo‐catalyst by POMs with super acidity and ultra‐stable structure. [ABSTRACT FROM AUTHOR]

Nanocrystalline mordenite (MOR) zeolites were hydrothermally synthesized in a single step with commercial cetyltrimethylammonium (CTA) hydroxide as the sole organic template, while the aluminum source was varied in a typical synthesis gel. CTA can effectively reduce the crystal growth of MOR zeolites, in some cases selectively in the a‐ and b‐directions of the unit cell. These nanocrystalline MOR zeolites do not only have a larger external surface area than their bulk counterparts prepared without CTA, but the Brønsted acid sites in the side‐pockets are also more accessible. The combination of the use of CTA and AlCl3 ⋅ 6H2O afforded the best‐performing catalyst with much improved activity in benzene alkylation and hydroconversion of n‐hexadecane (n‐C16). Modifying MOR synthesis with CTA hydroxide is a cheap and effective method to open up the one‐dimensional micropore system of mordenite, increasing the catalytic performance in hydrocarbon reactions. [ABSTRACT FROM AUTHOR]

The activation and functionalization of C−F bonds in various fluoroorganics were found to be a daunting task owing to their innate inertness. Harnessing the C−F bonds will alleviate the toxicity and environmental issues posed by them, and provide new pathways to access value‐added products. Although several strategies have been employed such as metal complexes, Brønsted acids, Lewis acids, and photocatalyst to activate the C−F bonds, however, the use of NHC or Metal‐NHC is relatively scarce. NHCs based catalytic C−F activation stands out owing to its easy accessibility, stability, and facile reactivity. Metal‐NHCs were exploited in hydrodefluorination, C−C, and C−B coupling reactions. Additionally, R−M(F)(NHC), an oxidative‐addition intermediate that was conveniently isolated allows to decode catalytic C−F functionalization pathways. This minireview provides the prominence of NHC and metal‐NHC in the area of catalytic C−F bond functionalization. [ABSTRACT FROM AUTHOR]

Stereoselective hydrogenation of α‐pinene over heterogenous catalysts under solvent‐free conditions is promising for biomass conversion but challenging. Herein, we prepared the Ru‐NiO/Hβ catalysts using chemical reduction and galvanic replacement methods. With the increase of Ni content, the selectivity of cis‐pinane was significantly improved. A high conversion of 100 % and a high cis‐pinane selectivity of 98 % were achieved after 4 h reaction at 80 °C. It has been verified that the addition of Ni can adjust the ratio of Brønsted and Lewis acid, regulate the hydrogen spillover between Ru and support, change the adsorption site of substrate and form steric hindrance effect. All these contribute to the better selectivity of the catalyst. In addition, catalysts presented good stability in the 900 h test. [ABSTRACT FROM AUTHOR]

The development of heterogeneous catalysts for light olefin production via a catalytic cracking has been crucially important due to the high demand of related products in industrial applications. Herein, we report the structural analysis of a germanium‐substituted hierarchical ferrierite zeolite obtained by one‐pot synthesis. This is the first report on an investigation of the synergistic effect of hierarchical structures and the one‐pot Ge‐substitution in a ferrierite framework on the catalytic cracking mechanism. Our findings exhibit that the existence of germanium in a hierarchical ferrierite framework can indeed reduce the Brønsted acid strength, facilitating a catalytic reaction with high light olefin selectivity (63 %) due to the elimination of side reactions, such as dimerization and aromatization, confirmed by in‐situ DRIFTS and DFT studies. This opens up the perspective of the development of metal substitution in an interconnected 8‐ and 10‐pore framework with hierarchical structures on the catalytic behaviors of light olefin production. [ABSTRACT FROM AUTHOR]

Visible‐light photocatalysis has advanced as a versatile tool in organic synthesis. However, attaining precise stereocontrol in photocatalytic reactions has been a longstanding challenge due to undesired photochemical background reactions and the involvement of highly reactive radicals or radical ion intermediates generated under photocatalytic conditions. To address this problem and expand the synthetic utility of photocatalytic reactions, a number of innovative strategies, including mono‐ and dual‐catalytic approaches, have recently emerged. Of these, exploiting chiral organocatalysis, such as enamine catalysis, iminium‐ion catalysis, Brønsted acid/base catalysis, and N‐heterocyclic carbene catalysis, to induce chirality transfer of photocatalytic reactions has been widely explored. This Review aims to provide a current, comprehensive overview of asymmetric photocatalytic reactions enabled by chiral organocatalysts published through June 2021. The substrate scope, advantages, limitations, and proposed reaction mechanisms of each reaction are discussed. This review should serve as a reference for the development of visible‐light‐induced asymmetric photocatalysis and promote the improvement of the chemical reactivity and stereoselectivity of these reactions. [ABSTRACT FROM AUTHOR]

Here, we describe the maximum production of 5‐HMF using glucose over Sn doped Ta2O5 in a binary solvent system. The analytical characterizations established that Sn4+ in the catalyst interacts with Ta2O5 and offers the Lewis acid sites favorable for glucose isomerization to fructose. Similarly, the Ta2O5 support offers both the Lewis and Brønsted acid sites to promote fructose dehydration to 5‐HMF. The catalyst provided favorable conditions for the sequential sugar(s) transformation, i. e. glucose isomerization followed by fructose dehydration, which resulted in a 5‐HMF yield as high as 57 % wt. and 80 % selectivity under modest reaction conditions in a water‐DMSO system using ST1 (1 % Sn on Ta2O5). The separate fructose to 5‐HMF conversion study verified the negligible influence of Sn on the dehydration reaction. Moreover, the catalyst's systematic sugar conversion enabled a >65 % fructose formation, which accounts for the enriched 5‐HMF synthesis. The neural network model best represented the 5‐HMF data (<4 % MAE for glucose and fructose conversions). [ABSTRACT FROM AUTHOR]

A bispyridylamine‐based hanging unit within the ligand framework of a newly synthesized iron porphyrin complex (Py2XPFe) can act, on the one hand, as a hydrogen bonding site to facilitate proton transfer in catalysis and, on the other hand, as coordination site for a second Lewis acidic metal center. The bispyridylamine group in close proximity of the iron porphyrin center is able to mediate electrocatalytic CO2 reduction in anhydrous MeCN. The hydrogen bonding interactions within the hanging group affect the kinetics of catalysis likely through stabilization of the [FeI(CO2H)]− intermediate, increasing the overall rate of catalysis when compared to the non‐functionalized analog, TMPFe (TMP=tetramesitylporphyrin). The rate constants (kapp) of the reduction reaction were calculated using the FOWA method which resulted in a higher TOFmax for the complex Py2XPFe compared with TMPFe in neat MeCN (1.7×102 vs. 1.1×101 s−1). The addition of weak Brønsted acids to the reaction mixture (TFE or PhOH) shows an increase in the rate of catalysis for both complexes, yet the Py2XPFe analog displays higher TOFmax at each relative acid concentration, suggesting the hanging group beneficially impacts the rate of catalysis in the presence of these proton sources. The addition of Lewis acidic Sc3+ to Py2XPFe also results in an increase in current density of the CO2 reduction reaction. Resonance Raman as well as 1H‐NMR spectroscopy indicates coordination to the pyridine substituents. [ABSTRACT FROM AUTHOR]

Designing efficient catalysts for glycerol hydrogenolysis to 1,3‐propanediol (1,3‐PDO), which involves the selective cleavage of the secondary C−O bond, is a challenging task. Current Pt−WOx‐based catalysts often provide low atom efficiency of W and Pt toward 1,3‐PDO production due to undesired catalyst structures. Herein, we fabricate the highly‐dispersed substantially uniform WOx species on inert α‐Al2O3 support by simple high‐temperature heat‐treatment, and the amount of Pt−WOx interface active sites could be adjusted by Pt loading, showing an excellent catalytic performance in glycerol hydrogenolysis at high concentration of glycerol, especially the unprecedented W efficiency (76 g1,3‐PDOgW−1 h−1) toward 1,3‐PDO. The high catalytic efficiency is attributed to the strong interaction between the isolated WO4 species and platinum, which could in‐situ generate the Brønsted acid sites during the reaction as evidenced by IR analysis with NH3 adsorption. [ABSTRACT FROM AUTHOR]

Zirconia supported WOx clusters with high acid strength and good stability are important solid acid catalysts in many reactions. However, conventional synthetic methods such as incipient‐wetness impregnation and co‐precipitation usually result in the products with low catalytic activity due to low surface area, uncontrollable and non‐homogeneous distribution of tungsten species. In this study, a facile multicomponent co‐assembly approach was utilized to straightforwardly synthesize ordered mesoporous WOx/ZrO2 composites (OMWZr) with mesopore size over 17 nm, pore volume of 0.13–0.18 cm3/g and surface area of 27.3–41.7 m2/g. The materials were composed of robust crystalline ZrO2 skeleton and well‐dispersed WOx clusters (polytungstates) in framework under the optimized conditions. The tungsten species were well stablized by the crystallized skeletons of mesoporous ZrO2, which can inhibit the growth of tetragonal ZrO2 but facilitate crystallization of monoclinic ZrO2. The states of tungsten species (monotungstates, polytungstates and crystalline WO3) can be precisely adjusted by their doping amount in framework and calcination temperature as well, which can further tune the surface acidity of OMWZr composites. Owing to the existence of numerous active surface WOx clusters generated over exposed surface of mesoporous ZrO2, the OMWZr catalysts not only show great spatial homogeneity of accessible Brønsted acid sites and feasible mass diffusion during catalytic reactions, but also display outstanding acid‐catalytic performance over hydrolysis reactions of benzaldehyde dimethyl acetal. The catalyst can be reused for more than 10 cycles, without reduction of catalytic activity and selectivity to benzaldehyde. [ABSTRACT FROM AUTHOR]

Supported‐phosphate‐catalysts (SPCs) are a versatile class of heterogeneous materials used in various industrially relevant processes including Fischer‐Tropsch synthesis (FTS), selective catalytic reduction (SCR) of NOx with NH3, and Guerbet reaction of C2H5OH to n‐C4H9OH. Herein, model SPCs synthesized by impregnating various supports with phosphoric acid were studied using in‐situ chemical probe temperature‐programmed‐desorption infrared spectroscopy. Hydroxylation of the catalyst surface was observed during the temperature ramp on all SPCs. This behavior was not observed on the bare supports during identical experiments. The results indicate that hydroxylation of the surface occurs via sacrificial hydrogen‐transfer reaction, where the chemical probe (NH3 or C2H5OH) can be utilized as the hydrogen‐donor. Results herein also show that the extent and the rate of hydrogen‐transfer reaction depend on the identity of the support, phosphate loading, and identity of the hydrogen‐donor molecule. Surface Brønsted acid sites (P−OH) do not contribute to the reaction and P=O surface sites are proposed as the active sites for the observed hydrogen‐transfer. Based on the current work, it is suggested that any catalytic reaction that involves hydrogenation over phosphate‐promoted or phosphate‐based catalysts needs to account for the surface‐mediated hydrogen‐transfer capability of the phosphate sites in the overall reaction mechanism. [ABSTRACT FROM AUTHOR]

Spatial confinement plays a significant role in selective adsorption and catalysis of molecular sieves. In this work, the adsorption behaviors of methanol in 8‐membered ring cage‐type molecular sieves DNL‐6 and SAPO‐42 were investigated by 13C solid‐state NMR (ssNMR) and density functional theory (DFT) calculations. Confinement‐induced spatial orientation of guest molecules in molecular sieves was revealed with considering both confined space and active centers. Confined space of double 8‐membered rings (D8R) in DNL‐6 favors the adsorption of methanol, accompanied by the methyl groups orientating to D8R space and the hydroxyl groups of methanol anchored by Brønsted acid site (BAS). [ABSTRACT FROM AUTHOR]

In this paper, the SCR properties of MIL‐88B(V) and MIL‐101(V) MOFs materials by hydrothermal synthesis were investigated, and the effect of the coordination and spatial topology of MOFs materials on the coordination state, chemical state and surface properties of V ions, as well as the relationship with SCR catalysis, were discussed. The results showed that the NO conversion of MIL‐88B(V) can be as high as 80 %, while those of MIL‐101(V) can only reach to 20 %, but the SCR reaction selectivity of both were excellent. The coordination structure and spatial topological structure of MOFs materials had a great influence on the coordination state, chemical state and surface properties of V ions, resulting in different SCR catalytic performance. The reaction performance of SCR was related to the structural properties of V3Ox units and followed the E‐R mechanism. The staggered and layer upon layer close‐packed structure of MIL‐88B(V) made the density of V3Ox unit cluster higher and the distance of adjacent V3Ox unit cluster smaller. More V5+ ions and V−O−V bonds can form more Brønsted acid sites, also was conducive to the progress of the SCR reaction. Although MIL‐88B(V) has insufficient high temperature stability, but its good SCR reaction selectivity and SCR catalytic performance at medium and low temperature can still have the application prospect of medium and low temperature industrial denitration in non‐electric industries. [ABSTRACT FROM AUTHOR]

In this paper, the SCR properties of MIL‐88B(V) and MIL‐101(V) MOFs materials by hydrothermal synthesis were investigated, and the effect of the coordination and spatial topology of MOFs materials on the coordination state, chemical state and surface properties of V ions, as well as the relationship with SCR catalysis, were discussed. The results showed that the NO conversion of MIL‐88B(V) can be as high as 80 %, while those of MIL‐101(V) can only reach to 20 %, but the SCR reaction selectivity of both were excellent. The coordination structure and spatial topological structure of MOFs materials had a great influence on the coordination state, chemical state and surface properties of V ions, resulting in different SCR catalytic performance. The reaction performance of SCR was related to the structural properties of V3Ox units and followed the E‐R mechanism. The staggered and layer upon layer close‐packed structure of MIL‐88B(V) made the density of V3Ox unit cluster higher and the distance of adjacent V3Ox unit cluster smaller. More V5+ ions and V−O−V bonds can form more Brønsted acid sites, also was conducive to the progress of the SCR reaction. Although MIL‐88B(V) has insufficient high temperature stability, but its good SCR reaction selectivity and SCR catalytic performance at medium and low temperature can still have the application prospect of medium and low temperature industrial denitration in non‐electric industries. [ABSTRACT FROM AUTHOR]

MIL‐101(Cr) with adjustable Brønsted acid density was prepared via post‐synthetic sulfation strategy, which was carried out with sulfuric acid in the presence of trifluoromethanesulfonic anhydride, using nitromethane as solvent. XRD, TG, EDS, XPS, IR, NH3‐TPD and acid‐base titration were used to characterize structure and acidity. Adopting conversion of ethanol as a probe reaction, gas‐solid catalytic characteristics on MIL‐101(Cr) and post‐synthetic sulfated MIL‐101(Cr) in a micro fixed‐bed reactor were studied by continuous feeding. Combined with the regulation of reaction parameters, selective production of ethylene (100 %) or diethyl ether (99 %) could be achieved. [ABSTRACT FROM AUTHOR]

The chemical liquid deposition modification can decorate the pore aperture size by external surface deposition, which is a very efficient way to further improve the shape‐selective performance of zeolites. Here, SAPO‐34 zeolite was modified with silica by chemical liquid deposition, and then was applied in MTO reaction. It was found the Brønsted acid of SiO2‐modified SAPO‐34 zeolite increased, mainly due to the transformation from Al‐OH to Si‐OH‐Al, which can promote the selectivity to light olefins in MTO reaction. After the chemical liquid deposition, the silica located on the external surface of SAPO‐34 zeolite, reduces the apparent diffusion coefficient of propylene, which will restrain the formation and diffusion of propylene. So the selectivity to ethylene and the ratio of ethylene to propylene were significantly increased over the SiO2‐modified SAPO‐34 in the MTO reaction. Furthermore, the increase of the reactive sites can prolong the lifetime of catalyst effectively. [ABSTRACT FROM AUTHOR]

The kinetic and thermodynamic features of indole N1‐ and C6‐alkylation reactions with (aza‐)quinone methides have been studied. The electrophilic reactivity of these quinone methides have also been compared for the first time by both experiments and DFT calculations. The indole N1‐alkylation is typically kinetically favorable, but the C6‐alkylation is more thermodynamically favorable. With suitable conditions, the C6‐alkylation could be achieved with high efficiency and selectivity. Among these quinone methides, the reactivity increases from aza‐p‐QMs to o‐QMs. The results not only provide access to a range of valuable triarylmethanes, but also guide future development of new reactions with these versatile electrophiles. [ABSTRACT FROM AUTHOR]

The cooperative catalysis of copper, silver, and Brønsted acid is presented as a new strategy for the intermolecular carboamination of arylalkenes. The catalytic regio‐ and chemoselective intermolecular carboamination of arylalkenes with allylic alcohols and nitriles provided a straightforward and efficient approach for preparing N‐acyl 4,5‐unsaturated amines. These amines can be used as synthetic organic synthons for the preparation of nitrogen‐containing five‐ and six‐membered heterocycles. During the functionalization reaction, synthetically useful functional groups, such as Cl, Br, and chloromethyl, remained intact. [ABSTRACT FROM AUTHOR]

The presence of alkali (Na+ or Li+) or alkali‐earth (Ca2+ or Mg2+) cations adjusting the acid‐base properties on amorphous silica‐alumina influences markedly the catalytic properties of supported Ni for 1‐butene dimerization. The low concentration of Brønsted acid sites on these catalysts reduces the double bond isomerization of butene and inhibits the formation of dimethylhexene as primary product. While the alkali and alkali‐earth cations act as weak Lewis acid sites, only Ni2+ sites are catalytically active for dimerization of 1‐butene. n‐Octene and methylheptene are formed selectively as primary products; dimethylhexene is a secondary product. The open environment of the Ni2+ sites does not induce different reaction pathways compared to Ni2+ in the pores of zeolites. [ABSTRACT FROM AUTHOR]

Brønsted solid acids have popularly been used as catalysts or supports for many hydrogenation reactions, while it is uncertain if their structural H species could significantly enhance velocity and reusability for these reactions. In this work, a series of tantalate‐supported silver catalysts Ag/MxH2–xTa2O6 (M=H, Li, Na, K, Sr) were prepared, along with abundant solid acid catalysts (Ag/Al2O3, Ag/SiO2−Al2O3, Ag/ZrO2−SO42−, and Ag/heteropolyacid). By assessing activity of a model reaction from p‐nitrophenol to the corresponding aniline together with an isotope comparative test (Ag/D2Ta2O6 and Ag/H2Ta2O6), a previously unknown route was uncovered, which involves that intrinsic proton H species of the Brønsted solid acid support directly participate in the formation of products. Meanwhile, Ag NPs could form an embedded distribution by exchanging with structural H species, responsible for the stabilization of catalytic active sites. The results reported here could give a deep understanding on proton chemistry of solid acids in construction of catalysts and/or supports in H‐participating reactions. [ABSTRACT FROM AUTHOR]

A highly water‐dispersible heterogeneous Brønsted acid surfactant was prepared by synthesis of a bi‐functional anisotropic Janus‐type material. The catalyst comprises ionic functionalities on one side and propyl‐SO3H groups on the other. The novel material was investigated as a green substitute of a homogeneous acidic phase transfer catalyst (PTC). The activity of the catalyst was investigated for the aqueous‐phase oxidation of cyclohexene to adipic acid with 30 % hydrogen peroxide even in a decagram‐scale. It can also be used for the synthesis of some other carboxylic acid derivatives as well as diethyl phthalate. [ABSTRACT FROM AUTHOR]

Methane dehydroaromatization (MDA) over Mo/HZSM‐5 has been hypothesized in literature to proceed via a two‐step mechanism: methane is first converted to ethylene on the molybdenum (Mo) functionality and then ethylene is oligomerized, cyclized and dehydrogenated on the Brønsted acid sites (BAS) of the HZSM‐5 support. This hypothesis is tested by studying the conversion of ethylene at the same conditions as used for MDA, namely 700 °C, atmospheric pressure, and by co‐feeding experiments with H2 and CH4. Our results suggest that ethylene is not the main intermediate for MDA, because the aromatic selectivities obtained from methane conversion are higher than selectivities measured during ethylene conversion. Furthermore, carbonaceous deposits formed during MDA have a lower density, are more hydrogenated and more active than the ones formed during ethylene aromatization (EDA). Similarly as for MDA, an activation period in which Mo carburizes to its active phase and an induction period, in which aromatics formation rates increase to their maximum are observed for ethylene conversion. The induction period, which was explained by the buildup of a hydrocarbon pool (HCP) is much faster with methane than with ethylene. This period, is attributed to a slow buildup of hydrocarbons, strongly adsorbed on Mo sites, because it is only observed with catalysts containing Mo. Hydrogen co‐feeding with ethylene leads to the formation of more reactive coke species and a significantly prolonged lifetime of the catalyst, but not to a faster buildup of the HCP. [ABSTRACT FROM AUTHOR]

To clarify the issue on Brønsted acidity enhancement by the presence of zinc species in H‐ZSM‐5 zeolite (G.D. Qi, et al. Angew. Chem.‐Int. Edit. 2016, 55, 15826), the influence of Zn2+ cationic species, introduced into the zeolite, on the strength of Brønsted acid sites (BAS) has been analyzed by solid‐state NMR and FTIR techniques using trimethylphosphine (TMP) and CO as probe molecules. Comparative analysis of the acidity for H‐ZSM‐5 and Zn2+/H‐ZSM‐5 zeolites has been performed. TMP adsorbed on both zeolite samples exhibits same signals at 6.3 and −4.5 ppm in 1H and 31P MAS NMR spectra, respectively, assigned to protonated TMP. FTIR spectroscopy has shown that both zeolite samples, H‐ZSM‐5 and Zn2+/H‐ZSM‐5, display the same red frequency shift (ΔνOH⋅⋅⋅CO=−318 cm−1) of the O−H stretching band and the same blue frequency shift (ΔνCO=+32 cm−1) of the CO stretching band for CO adsorption complex with BAS. The results obtained do not provide any evidence for the existence of some specific BAS with enhanced acid strength for Zn2+‐exchanged zeolite compared to the strength inherent to pure acid‐form zeolite. It is thus inferred the strength of BAS in H‐ZSM‐5 zeolite is not affected by the modification of the zeolite with Zn2+ cationic species. [ABSTRACT FROM AUTHOR]

Amorphous silica‐aluminas (ASAs), possessing both Brønsted acid sites (BAS) and Lewis acid sites (LAS), are important bifunctional catalysts in various industrial applications. Solid‐state NMR spectroscopy has been widely used for characterizing the local structure and the surface sites of ASAs with probe molecules. In this work, four‐, five‐ and six‐coordinated Al species have been observed on the flame‐made ASAs by 27Al MQ MAS NMR experiment. 1H/27Al TRAPDOR MAS NMR experiments confirmed that surface Al species contribute to the formation of BAS and protonate ammonia probe molecules. The adsorption of ammonia on Lewis acidic Al sites (δ1H=3.0 ppm) was evidenced by various 1H MAS NMR experiments on samples dehydrated at different temperatures, allowing the distinction from ammonium ions (δ1H=6.7 ppm) formed at BAS. The signal of ammonia adsorbed on LAS increased with increasing Al content in the ASAs. These properties together with the absence of pore diffusional constraints render the flame‐made ASAs excellent catalysts for cyclohexanol dehydration and the conversion of glyceraldehyde in ethanol to ethyl lactate, outperforming the performance of other ASAs or zeolites. [ABSTRACT FROM AUTHOR]

Acidic zeolites, especially faujasites, efficiently promote the intramolecular cyclization of aryl propynoates and propynethioates, which produces coumarins and thiocoumarins, usually in high yields. Comparison with homogeneous Lewis or BrØnsted acids and with heterogeneous related sieve materials revealed the prevalence of zeolites exhibiting large cage‐type pores (H‐USY) for such cyclizations. Various substituents proved compatible with the cyclization process, leading to a variety of substituted coumarins and thiocoumarins (20 examples, 30–99 %). [ABSTRACT FROM AUTHOR]

A comparative study was reported for both the effects of shape‐confined cubic Pd particle size (8, 13, and 21 nm) and surface property of most commonly used supports (SiO2, Al2O3, and silica‐alumina) on catalytic performance in the chemoselective hydrogenation of three model bio‐oil chemicals (benzaldehyde, acetophenone, and butyrophenone). The results showed that the size of Pd particles could be more associated with the hydrogenation reaction than acidities of the supports. Smaller size of Pd particles, regardless of the type of the support, provided the higher catalytic performance. XPS data showed that the electronic properties of Pd particles were similar, therefore, the possible reasons were the higher fraction of Pd atoms on corner in smaller particles, the lower accessibility of hydrogen atom to reactant on bigger particles, and the more low‐coordinated sites in the small‐size particles due to the short‐range ordering. In addition, Pd/SA catalysts (Brønsted acid sites on the support) showed the highest conversion and TOF compared to Pd/Al2O3 and Pd/SiO2 catalysts. This might be due to the enhanced the diffusion rates of the chemicals on the surface of the catalysts although they could not induce the ionic effect from the metal surface. Pd/SiO2 catalysts performed better than Pd/Al2O3 catalysts (Lewis acid sites on the support). The flexible SiOH groups on surface made the easy interaction with the metal particles and promote the reaction. [ABSTRACT FROM AUTHOR]

Selective cleavage of secondary C−O bond is an important yet challenging strategy in glycerol valorization, and the product 1,3‐propanediol (1,3‐PDO) is of great value in polyester industry. Herein, we report a series of Pt/WOx/Al2O3 catalysts for selective hydrogenolysis of glycerol in a fixed‐bed reactor and obtain the highest space‐time yield of 1,3‐PDO (191.7*10−3 g1,3‐PDO h−1 g−1cat.) to date. Both Pt and W have substantial effects on the 1,3‐PDO yield with the optimum Pt/W atomic ratio of 1/2∼1/4. Spectroscopy characterizations as well as chemisorption experiments reveal that at the medium domain size of WOx, hydrogen spillover can take place to the greatest extent due to the improved dispersion of Pt and the suitable reducibility of WOx. Dehydration/dehydrogenation tests of 2‐butanol suggest that strong Brønsted acid sites are created via hydrogen dissociation at the Pt−WOx interface and spillover to the neighboring oxygen atom. Such in situ formed protons are critical to the selective cleavage of secondary C−O bonds of polyols. [ABSTRACT FROM AUTHOR]

The methylation of hexamethylbenzene with methanol is one of the key reactions in the methanol‐to‐olefins hydrocarbon pool reaction cycle taking place over the industrially relevant H‐SAPO‐34 zeolite. This methylation reaction can occur either via a concerted or via a stepwise mechanism, the latter being the preferred pathway at higher temperatures. Herein, we systematically investigate how a complex reaction environment with additional water molecules and higher concentrations of Brønsted acid sites in the zeolite impacts the reaction mechanism. To this end, first principle molecular dynamics simulations are performed using enhanced sampling methods to characterize the reactants and products in the catalyst pores and to construct the free energy profiles. The most prominent effect of the dynamic sampling of the reaction path is the stabilization of the product region where water is formed, which can either move freely in the pores of the zeolite or be stabilized through hydrogen bonding with the other protic molecules. These protic molecules also stabilize the deprotonated Brønsted acid site, created due to the formation of the heptamethylbenzenium cation, via a Grotthuss‐type mechanism. Our results provide fundamental insight in the experimental parameters that impact the methylation of hexamethylbenzene in H‐SAPO‐34, especially highlighting and rationalizing the crucial role of water in one of the main reactions of the aromatics‐based reaction cycle. [ABSTRACT FROM AUTHOR]

Dual catalysis constitutes a growing field of the organic synthesis. It is a useful methodology, which allows for a discovery of new and more efficient transformations. This concept article describes tandem reactions, which comprise of an isomerization of the double bond and following transformation, whereby a combination of a homogeneous metal catalyst and Brønsted acid is used. The aim is to highlight the versatility of this catalyst combination. [ABSTRACT FROM AUTHOR]

Extrinsic Brønsted acid sites (BAS) on zeolites are generated on NaY upon exposure to organic acids through an ion exchange process. However, the acid‐base chemistry of species adsorbed on the zeolites is largely unexplored. In this work, organic acids with varying acidity are employed to investigate the proton‐transfer displacement within the micropores of NaY. The direction and degree of the displacement reactions are monitored by in situ transmission Fourier transform infrared (FTIR) spectroscopy. Two organic acids are sequentially introduced to NaY, and the direction and extent of the displacement reaction are followed by the diagnostic vibrational band of the adsorbed carboxylate species, i. e., ν([O−C−O]−). Stronger acids are able to displace dissociatively adsorbed weaker acids on NaY, which is analogous to the solution‐phase acid‐base chemistry favoring the formation of weaker acids by stronger acids. The gas phase deprotonation energy correlates more closely with displacement reaction than pKa, which is explicitly defined in the aqueous solution of acids. A thermochemical cycle is constructed to rationalize the observation that acid‐base reactions in the zeolite pores could be predicted with the gas phase acidity of compounds involved in the displacement reactions. [ABSTRACT FROM AUTHOR]

In this study, we report that intercalation of tin into montmorillonite clay (Sn‐MMT) boosts catalytic activity for the synthesis of polyoxymethylene dimethyl ethers, a promising diesel fuel additive. This increase in activity is attributed to the formation of a hierarchical catalyst displaying high surface area with accessible Brønsted and Lewis acid sites. Extensive characterization such as MAS‐NMR, XRD and in‐situ DRIFTS confirmed that tin insertion induced reorganization of the clay layers into a disorganized house‐of‐cards structure. It also revealed that tin resided between the clay layers as defective SnO2 nanocrystals stabilized by the negative charge of MMT. The source of acidity in Sn‐MMT was studied by comparing it with two similar materials, namely Sn(OH)4, and thermally treated Sn‐MMT. Low activity measured for isolated hydroxylated SnO2 nanoparticles illustrates the importance of having clay and tin in close proximity. Meanwhile, deactivation upon thermal treatment occurred via sintering of the tin phase and diffusion of the protons inside the layers. Sn‐MMT acidity is attributed to the combination of Si−OH−Al groups, formed as a by‐product of SnO2 crystallization, and undercoordinated Sn surface sites, stabilized by the negative charge of MMT. [ABSTRACT FROM AUTHOR]

Aqueous‐phase conversion of glyceraldehyde to lactic acid was investigated over Nb2O5, TiO2, ZrO2 and SnO2 in a fixed‐bed up‐flow reactor. Special attention was given to the catalysts acidity regarding the type, amount, strength and tolerance to water of surface acid sites. These sites were assessed by infrared spectroscopy of pyridine adsorbed on dehydrated and hydrated catalysts as well as by isopropanol decomposition. It was found that Nb2O5 and TiO2 have the highest fraction of water‐tolerant Lewis acid sites (40 and 47 %), while only 6 % was estimated for ZrO2. No relevant Lewis acidity was observed on SnO2, but it was noticed the presence of strong base sites. The transformation of glyceraldehyde into lactic acid proceeded via a cascade reaction in which glyceraldehyde is firstly dehydrated to pyruvaldehyde, followed by its rearrangement to lactic acid with the addition of a water molecule. The dehydration step occurs on Brønsted acid sites and/or on water‐tolerant Lewis acid sites. These latter sites also determine the selectivity to lactic acid. Strong base sites promote glyceraldehyde fragmentation leading to formaldehyde with high selectivity. [ABSTRACT FROM AUTHOR]