Direct Conversion of Syngas into Methyl Acetate,Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether

Selective conversion of syngas (CO/H₂) into C₂₊ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu‐Zn‐Al oxide/H‐ZSM‐5 and zeolite mordenite (H‐MOR) catalysts separated by quartz wool (denoted as Cu‐Zn‐Al/H‐ZSM‐5|H‐MOR) and also at higher temperatures (603–643 K) without significant deactivation using spinel‐structured ZnAl₂O₄|H‐MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl₂O₄|H‐MOR|ZnAl₂O₄ gives ethanol as the major product, while ethylene is formed with a layer‐by‐layer ZnAl₂O₄|H‐MOR|ZnAl₂O₄|H‐MOR combination. Close proximity between ZnAl₂O₄ and H‐MOR increases ethylene selectivity to 65 %.     

Template‐Synthesized Porous Silicon Carbide as an Effective Host for Zeolite Catalysts

A facile method has been developed for the fabrication of porous silicon carbide (SiC) by means of sintering a mixture of SiC powder and carbon pellets at a relatively lower temperature, that is, 1450 °C, in air. The pore density and the total pore volume of the resulting porous SiC could be tuned by changing the initial SiC/C weight ratio. The structure evolution and the associated property changes during the preparation were examined through X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, ²⁹Si magic‐angle spinning (MAS) NMR spectroscopy, and mercury‐intrusion porosimetry analyses. Silica and SiO_xC_y ceramics formed in situ during the calcination process acted as binders of the porous SiC grains. The porous SiC can be used as a host for the growth of ZSM‐5 zeolite crystals to form the ZSM‐5/porous‐SiC composite material. After loading another catalytic active component of molybdenum, a novel catalytic material, Mo‐ZSM‐5/porous‐SiC, was obtained, which exhibited improved catalytic activity in the methane dehydroaromatization reaction.     

Zr–Zeolite Beta: A New Heterogeneous Catalyst System for the Highly Selective Cascade Transformation of Citral to (±)‐Menthol

Minty green : Zr–zeolite beta (Zr‐beta) directs the one‐pot catalytic cascade transformation of citral to menthols with high diastereoselectivity. The solid catalyst, a bifunctional Ni/Zr‐beta or a composite Zr‐beta–Ni/MCM‐41 system, is easily recovered and reused in this green synthetic method (see figure).

     

Ultrafast Encapsulation of Metal Nanoclusters into MFI Zeolite in the Course of Its Crystallization: Catalytic Application for Propane Dehydrogenation

Encapsulating metal nanoclusters into zeolites combines the superior catalytic activity of the nanoclusters with high stability and unique shape selectivity of the crystalline microporous materials. The preparation of such bifunctional catalysts, however, is often restricted by the mismatching in time scale between the fast formation of nanoclusters and the slow crystallization of zeolites. We herein demonstrate a novel strategy to overcome the mismatching issue, in which the crystallization of zeolites is expedited so as to synchronize it with the rapid formation of nanoclusters. The concept was demonstrated by confining Pt and Sn nanoclusters into a ZSM-5 (MFI) zeolite in the course of its crystallization, leading to an ultrafast, in situ encapsulation within just 5 min. The Pt/Sn-ZSM-5 exhibited exceptional activity and selectivity with stability in the dehydrogenation of propane to propene. This method of ultrafast encapsulation opens up a new avenue for designing and synthesizing composite zeolitic materials with structural and compositional complexity.     

醋酸钯和苯胂酸协同催化苯甲腈水合制备苯甲酰胺

以醋酸钯和苯胂酸(物质的量之比nPd∶nAs=3∶2)作为协同催化剂,用于催化苯甲腈水合制备苯甲酰胺。在不额外添加有机溶剂条件下,利用过量苯甲腈兼做溶剂,该反应获得了99%的高产率和100%的苯甲酰胺选择性以及高达186 mol·kg-1·h-1的时空收率,循环反应5轮未发现明显的活性与选择性的降低,催化剂具有良好的循环使用性能。产物的结晶分离研究结果表明苯甲酰胺在0℃的析出百分比为73%,简单过滤即可收集。     

Widening Synthesis Bottlenecks: Realization of Ultrafast and Continuous‐Flow Synthesis of High‐Silica Zeolite SSZ‐13 for NOx Removal

Characteristics of zeolite formation, such as being kinetically slow and thermodynamically metastable, are the main bottlenecks that obstruct a fast zeolite synthesis. We present an ultrafast route, the first of its kind, to synthesize high‐silica zeolite SSZ‐13 in 10 min, instead of the several days usually required. Fast heating in a tubular reactor helps avoid thermal lag, and the synergistic effect of addition of a SSZ‐13 seed, choice of the proper aluminum source, and employment of high temperature prompted the crystallization. Thanks to the ultra‐short period of synthesis, we established a continuous‐flow preparation of SSZ‐13. The fast‐synthesized SSZ‐13, after copper‐ion exchange, exhibits outstanding performance in the ammonia selective catalytic reduction (NH₃‐SCR) of nitrogen oxides (NO_x), showing it to be a superior catalyst for NO_x removal. Our results indicate that the formation of high‐silica zeolites can be extremely fast if bottlenecks are effectively widened.     

Direct and Highly Selective Conversion of Synthesis Gas into Lower Olefins: Design of a Bifunctional Catalyst Combining Methanol Synthesis and Carbon–Carbon Coupling

The direct synthesis of lower (C₂ to C₄) olefins, key building‐block chemicals, from syngas (H₂ /CO), which can be derived from various nonpetroleum carbon resources, is highly attractive, but the selectivity for lower olefins is low because of the limitation of the Anderson–Schulz–Flory distribution. We report that the coupling of methanol‐synthesis and methanol‐to‐olefins reactions with a bifunctional catalyst can realize the direct conversion of syngas to lower olefins with exceptionally high selectivity. We demonstrate that the choice of two active components and the integration manner of the components are crucial to lower olefin selectivity. The combination of a Zr–Zn binary oxide, which alone shows higher selectivity for methanol and dimethyl ether even at 673 K, and SAPO‐34 with decreased acidity offers around 70 % selectivity for C₂–C₄ olefins at about 10 % CO conversion. The micro‐ to nanoscale proximity of the components favors the lower olefin selectivity.     

Large Zeolite H‐ZSM‐5 Crystals as Models for the Methanol‐to‐Hydrocarbons Process: Bridging the Gap between Single‐Particle Examination and Bulk Catalyst Analysis

The catalytic, deactivation, and regeneration characteristics of large coffin‐shaped H‐ZSM‐5 crystals were investigated during the methanol‐to‐hydrocarbons (MTH) reaction at 350 and 500 °C. Online gas‐phase effluent analysis and examination of retained material thereof were used to explore the bulk properties of large coffin‐shaped zeolite H‐ZSM‐5 crystals in a fixed‐bed reactor to introduce them as model catalysts for the MTH reaction. These findings were related to observations made at the individual particle level by using polarization‐dependent UV‐visible microspectroscopy and mass spectrometric techniques after reaction in an in situ microspectroscopy reaction cell. Excellent agreement between the spectroscopic measurements and the analysis of hydrocarbon deposits by means of retained hydrocarbon analysis and time‐of‐flight secondary‐ion mass spectrometry of spent catalyst materials was observed. The obtained data reveal a shift towards more condensed coke deposits on the outer zeolite surface at higher reaction temperatures. Zeolites in the fixed‐bed reactor setup underwent more coke deposition than those reacted in the in situ microspectroscopy reaction cell. Regeneration studies of the large zeolite crystals were performed by oxidation in O₂/inert gas mixtures at 550 °C. UV‐visible microspectroscopic measurements using the oligomerization of styrene derivatives as probe reaction indicated that the fraction of strong acid sites decreased during regeneration. This change was accompanied by a slight decrease in the initial conversion obtained after regeneration. H‐ZSM‐5 deactivated more rapidly at higher reaction temperature.     

Central Doping of a Foreign Atom into the Silver Cluster for Catalytic Conversion of CO2 toward C−C Bond Formation

Clusters with an exact number of atoms are of particular interest in catalysis. Their catalytic behaviors can be potentially altered with the addition or removal of a single atom. Now the effects of doping with a single foreign atom (Au, Pd, and Pt) into the core of an Ag cluster with 25 atoms on the catalytic properties are explored, where the foreign atom is protected by 24 Ag atoms (Au@Ag₂₄, Pd@Ag₂₄, and Pt@Ag₂₄). The central doping of a single atom into the Ag₂₅ cluster has a substantial influence on the catalytic performance in the carboxylation reaction of CO₂ with terminal alkyne through C?C bond formation to produce propiolic acid. These studies reveal that the catalytic properties of the cluster catalysts can be dramatically changed with the subtle alteration by a single atom away from the active sites.     

Oxidative Conversion of Glucose to Formic Acid as a Renewable Hydrogen Source Using an Abundant Solid Base Catalyst

Formic acid is one of the most desirable liquid hydrogen carriers. The selective production of formic acid from monosaccharides in water under mild reaction conditions using solid catalysts was investigated. Calcium oxide, an abundant solid base catalyst available from seashell or limestone by thermal decomposition, was found to be the most active of the simple oxides tested, with formic acid yields of 50 % and 66 % from glucose and xylose, respectively, in 1.4 % H₂O₂ aqueous solution at 343 K for 30 min. The main reaction pathway is a sequential formation of formic acid from glucose by C−C bond cleavage involving aldehyde groups in the acyclic form. The reaction also involves base-catalyzed aldose-ketose isomerization and retroaldol reaction, resulting in the formation of fructose and trioses including glyceraldehyde and dihydroxyacetone. These intermediates were further decomposed into formic acid or glycolic acid. The catalytic activity remained unchanged for further reuse by a simple post-calcination.     

Dual‐Mesoporous ZSM‐5 Zeolite with Highly b‐Axis‐Oriented Large Mesopore Channels for the Production of Benzoin Ethyl Ether

Dual‐mesoporous ZSM‐5 zeolite with highly b axis oriented large mesopores was synthesized by using nonionic copolymer F127 and cationic surfactant CTAB as co‐templates. The product contains two types of mesopores—smaller wormlike ones of 3.3 nm in size and highly oriented larger ones of 30–50 nm in diameter along the b axis—and both of them interpenetrate throughout the zeolite crystals and interconnect with zeolite microporosity. The dual‐mesoporous zeolite exhibits excellent catalytic performance in the condensation of benzaldehyde with ethanol and greater than 99 % selectivity for benzoin ethyl ether at room temperature, which can be ascribed to the zeolite lattice structure offering catalytically active sites and the hierarchical and oriented mesoporous structure providing fast access of reactants to these sites in the catalytic reaction. The excellent recyclability and high catalytic stability of the catalyst suggest prospective applications of such unique mesoporous zeolites in the chemical industry.     

A Supported Copper Hydroxide on Titanium Oxide as an Efficient Reusable Heterogeneous Catalyst for 1,3‐Dipolar Cycloaddition of Organic Azides to Terminal Alkynes

An easily prepared supported copper hydroxide on titanium oxide (Cu(OH)_x/TiO₂) showed high catalytic performance for the 1,3‐dipolar cycloaddition of organic azides to terminal alkynes in non‐polar solvents under anaerobic conditions. The reactions of various combinations of organic azides (four examples, including aromatic and aliphatic ones) and terminal alkynes (eleven examples, including aromatic, aliphatic, and double bond‐containing ones) exclusively proceeded to give the corresponding 1,4‐disubstituted‐1,2,3‐triazole derivatives in a completely regioselective manner. For the transformation of benzyl azide and ethynylbenzene with 0.12 mol % of Cu(OH)_x/TiO₂, the turnover frequency was 505 h^?1 and the turnover number reached up to 800. These values were the highest among those with previously reported heterogeneous catalysts including Cu(OH)_x/Al₂O₃. The observed catalysis was truly heterogeneous and the retrieved catalyst after the reaction could be reused at least three times with retention of its high catalytic performance. It was confirmed by the UV/Vis spectrum of Cu(OH)_x/TiO₂ and the amount of diyne formed that the Cu^II species in Cu(OH)_x/TiO₂ were reduced to Cu^I species by the alkyne–alkyne homocoupling at the initial stage of the reaction (during the pretreatment of Cu(OH)_x/TiO₂ with an alkyne). The catalytic reaction rate for the 1,3‐dipolar cycloaddition linearly increased with an increase in the amount of in situ generated Cu^I species. Therefore, the in situ generated Cu^I species would be the catalytically active species for the present 1,3‐dipolar cycloaddition.