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Mechanistic insight and measurements of apparent kinetics for productive and non-productive reaction pathways guide the development of semi-batch reactors and conditions for stable production of carboxylic acids and diacids over supported tungstate catalysts.

Oxidative cleavage of carbon–carbon double bonds (C═C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, nontoxi...

Ce-incorporated MoVTeNbO catalysts were developed to enhance ethylene productivity of oxidative dehydrogenation of ethane (ODHE) to ethylene. Structural characterizations (XRD, TEM, STEM, Raman, and UV–vis DRS) and DFT calculations revealed that Ce atoms were incorporated into MoVTeNbO framework with maintaining its unique structure (M1 phase), which is active phase for ODHE. The reducibility of the catalysts was enhanced and both V5+ and the lattice oxygen species available to ODHE reaction were enriched by incorporation of Ce, confirmed by TPR, XPS, and pulse injection method, respectively. These improved properties enhanced the conversion of ethane while maintaining their excellent selectivity to ethylene for MoVTeNbCeO catalysts. It is noteworthy that 56.2% of ethane conversion and 95.4% of ethylene selectivity were retained for 200 h over MoVTeNbCeO-0.1 catalyst. Ethylene productivity was calculated to be 1.11 kgC2H4/kgcat h. The developed catalyst exhibits substantial level of ethylene productivity and stability having the possibility with low production of COx to make a step forward for industrialization of oxidative dehydrogenation of ethane.

A combination of in situ XANES, temperature programmed oxidation, kinetic and density functional theory results demonstrate that the d-band centers (ed) of Au and Pt metals are upshifted when 39.9 V m-1 of electric field is applied. This leads to the enhancement of the adsorption strength of CO on both metals, and, thus, results in the promotion (+15%) and the depression (-23%) of CO conversions on Au and Pt, respectively, in the CO oxidation.

Basic lithium phosphate (B-LPO) catalyst selectively produces unsaturated alcohols from epoxides. The catalytic activity of B-LPO is known to originate from appropriate acidic-basic properties, but no details were available on the structure of the active site. In this study, experimental methods and DFT calculations were performed in an attempt to identify the active surface structure of B-LPO for the isomerization of 2,3-epoxybutane to 3-buten-2-ol. The experimental results showed that exchanged Na ions in B-LPO suppressed the formation of an acid-catalyzed by-product (methyl ethyl ketone). In addition, H2O had a negative effect on the formation of 3-buten-2-ol due to the preoccupation of the active site. DFT calculations in conjunction with these experimental observations showed that the most plausible active surface for the formation of 3-buten-2-ol is the (001) surface of LPO whose acidic proton is exchanged with Na atom. On this surface, the under-coordinated Li atoms and the surface P O groups are exposed, and these play a role in activating the C O bond of an epoxide ring, and in receiving a proton from the terminal carbon, respectively.

Conversion of carbon dioxide for producing useful chemicals is an attractive method to reduce greenhouse gas emissions and to produce sustainable chemicals. However, the thermodynamic stability of CO₂ necessitates high levels of energy consumption for its conversion to chemicals. Here, we suggest a new catalytic system with an alternative heating system allowing for minimal energy consumption during CO₂ conversion. In this system, electrical energy is transferred as heat energy to the metal supported on carbon catalyst. Fast ramping rates allow for high operating temperatures (Tapp=250 °C) to be reached within 5 minutes, leading to an 80-fold lowering of energy consumption in methane reforming using CO₂ (DRM). In addition, the consumed energy normalized by time during DRM reaction in current-assisted catalysis is 6-fold lower (11.0 kJ·min-1) than conventional heating systems (68.4 kJ·min-1).

The reaction mechanism of glycerol hydrogenolysis to 1,2-propanediol over a spinel CuCr2 O4 catalyst was investigated by using DFT calculations. Theoretical models were developed from the results of experimental characterization. Adsorption configurations and energetics of the reactant, intermediates, final product, and transition states were calculated on Cu(1 1 1) and CuCr2 O4 (1 0 0). Based on our DFT results, we found that the formation of acetol is preferred to that of 3-hydroxypropionaldehyde thermodynamically and kinetically on both surfaces. For glycerol hydrogenolysis to 1,2-propanediol, the CuCr2 O4 surface is less exothermic but more kinetically favorable than the Cu surface. The low activation barrier during the reaction on the CuCr2 O4 surface is attributed to the unique surface structure; the cubic spinel structure provides a stable adsorption site on which reactants are allowed to be dehydrated and hydrogenated easily with the characteristic adsorption configuration. The role of the Cu and Cr atoms in a CuCr2 O4 surface were revealed. The results of reaction tests supported our theoretical calculations.

Selective methane oxidation is one of the key challenges in modern chemistry. To increase the value-added chemical production, the oxidation state of active metals should be easily converted to oxidized or reduced states in order to adsorb or provide an oxygen atom efficiently into methane. Here, we firstly report that lithium incorporating molybdenum oxide with silica supports significantly enhances HCHO production in virtue of redox-driven restructuring of active molybdenum sites. In reduction conditions under CH4 flow, lithium ions are inserted into the molybdenum-oxide phase by forming lithium molybdenum oxide (LiyMoO3) nanoclusters and conversely extracted by O2 oxidation. Due to the redox migration of lithium ions and reconstruction of LiyMoO3 nanoclusters under the reaction process, the oxidation state of active molybdenum centers is effectively controlled to both oxidized and reduced states. These findings provide insight into the distinct role of lithium ions in various catalytic systems and suggest new strategies for developing active sites for selective oxidation area.

Si-(OH)-Al groups of amorphous aluminosilicate have been known to play important roles in acid-catalyzed reactions. However, there is a lack of theoretical understanding on the catalytic function of the acid sites and reaction mechanisms on the amorphous aluminosilicate surface. In this study, the preferred glycerol dehydration mechanism on Si-(OH)-Al sites was investigated via density functional theory calculation, and compared to experimental results. An amorphous aluminosilicate surface was constructed based on the β-cristobalite crystal structure, and adsorption and activation energies were calculated for each elementary step in the glycerol dehydration at Si-(OH)-Al sites. It was found that when the primary OH group of glycerol is adsorbed on Bronsted proton (Si-(OH)-Al sites), the adsorption strength is too strong to convert to acetol. On the other hand, the secondary OH group of glycerol is adsorbed with a relatively moderate strength at the acid site, which then leads to favorable production of 3-hydroxypropionaldehyde (3-HPA). Consequently, the 3-HPA is readily dehydrated into acrolein and water due to its reactive properties. Therefore, glycerol seemed to be preferentially converted into acrolein on amorphous aluminosilicate during dehydration. In order to verify the preferential formation of acrolein, catalytic activity test was experimentally conducted. The amorphous aluminosilicate catalyst exhibited remarkable selectivity for acrolein (46.5%), which supported our theoretical approach. In addition, the adsorbed and polymerized glycerol on the used catalyst surface was identified via 13C NMR. This suggests that when glycerol is too strongly adsorbed, it can be transformed into coke during dehydration. Combining our theoretical and experimental observations, it was concluded that strongly adsorbed glycerol gives rise to not only a lower level of conversion but also coke deposition on the amorphous aluminosilicate surface. Comparative investigation of aluminosilicate and H-ZSM-5 zeolite gave new light on that the adsorption structure, adsorption energy, and reaction mechanism are altered by silanol groups on the aluminosilicate surface, although the active site (Si-(OH)-Al) of aluminosilicate is similar to that of H-ZSM-5 zeolite.

Catalytic activity was efficiently tuned via manipulating the electronic state of a catalyst, induced by a facile doping method in a metal/graphene system. The strategy was proven to be applicable to not only transition metal but also noble metal catalysts in CO hydrogenation and 4-nitrophenol reduction.

Due to its cost effectiveness and eco-friendliness, oxydehydration of glycerol is currently attracting considerable attention. In an attempt to develop an efficient catalyst for the reaction, tungsten-incorporated molybdenum vanadium mixed oxide (MoVW) catalysts were designed on the basis of computational calculations and mechanistic insights. By incorporating tungsten into molybdenum vanadium mixed oxide structure, the catalysts are active and selective not only for the dehydration of glycerol but also for the subsequent oxidation of acrolein to acrylic acid. Through DFT calculations, we confirmed that tungsten species induced a change in the electron density of neighboring atoms, which leads to selective production of acrylic acid. Structural characterization demonstrates that the structure of such MoVW catalysts is similar to that of DFT models. The incorporated tungsten species enhanced the acid and redox properties of the catalyst, leading to high selectivity for acrylic acid (30.5%). It not only ind...

Developing a catalyst to resolve deactivation caused from coke is a primary challenge in the dehydration of glycerol to acrolein. An open-macropore-structured and Brønsted-acidic catalyst (Marigold-like silica functionalized with sulfonic acid groups, MS-FS) was synthesized for the stable and selective production of acrolein from glycerol. A high acrolein yield of 73% was achieved and maintained for 50 h in the presence of the MS-FS catalyst. The hierarchical structure of the catalyst with macropores was found to have an important effect on the stability of the catalyst because coke polymerization and pore blocking caused by coke deposition were inhibited. In addition, the behavior of 3-hydroxypropionaldehyde (3-HPA) during the sequential dehydration was studied using density functional theory (DFT) calculations because 3-HPA conversion is one of the main causes for coke formation. We found that the easily reproducible Brønsted acid sites in MS-FS permit the selective and stable production of acrolein. This is because the reactive intermediate (3-HPA) is readily adsorbed on the regenerated acid sites, which is essential for the selective production of acrolein during the sequential dehydration. The regeneration ability of the acid sites is related not only to the selective production of acrolein but also to the retardation of catalyst deactivation by suppressing the formation of coke precursors originating from 3-HPA degradation.

The conversion of lignocellulose is a crucial topic in the renewable and sustainable chemical industry. However, cellulose from lignocellulose is not soluble in polar solvents, and is, therefore, difficult to convert into value-added chemicals. A strategy to overcome this drawback is the use of mesoporous carbon, which enhances the affinity between the cellulose and the catalyst through its abundant functional groups and large uniform pores. Herein, we report on the preparation of a Pt catalyst supported on a type of 3D mesoporous carbon inspired by Echinometra mathae (Pt/CNE) to enhance the interaction between the catalyst and a nonsoluble reactant. In the hydrolytic hydrogenation of cellulose, the abundant oxygen groups of CNE facilitated the access of cellulose to the surface of the catalyst, and the open pore structure permits cello-oligomers to effectively diffuse to the active sites inside the pore. The highly dispersed Pt performed dual roles: hydrolysis by in situ generating protons from H2 or water as well as effective hydrogenation. The use of the Pt/CNE catalyst resulted in an approximately 80 % yield of hexitol, the best performance reported to date. In direct conversion of hardwood powder, the Pt/CNE shows good performance in the production of sugar alcohols (23 % yield). We expect that the open-structured 3D carbon will be widely applied to the conversion of various lignocellulosic materials.

The production of di-n-butyl-ether (DNBE), for use as a blending agent in diesel fuel, is very attractive because the reactant (n-butanol) can be readily produced by the fermentation of bio-derivatives. The dehydration of n-butanol is known to show diffusion-limited characteristics on porous catalysts, such as zeolites or mesoporous supported catalysts. In order to overcome this limitation, herein, we synthesized silica spheres (DSS) with three-dimensional (3D) open pores by a hydrothermal reaction for use as a catalyst for the dehydration of n-butanol. In addition, supported heteropolyacid (PW) catalysts were also prepared on various porous silicas, DSS, SBA-15 and microporous silica (mi-S), to investigate the effect of 3D pore structures on the conversion of n-butanol to DNBE against 2D mesoporous and microporous materials by quantitative calculation. PW/DSS showed the best performance among the catalysts at various temperatures (453, 473, and 493 K). The extent of catalytic performance enhancement was quantified by calculating the effectiveness factor ( η ) based on kinetics data. The η values for PW/DSS, PW/SBA, and PW/mi-S were determined to be 0.83, 0.63 and 0.52, respectively.

The development of solid acid catalysts that contain a high density of Brønsted acid sites with suitable acidity, as well as a long lifetime, is one of great challenges for the efficient dehydration of glycerol to acrolein. Herein, we report on a mesoporous siliconiobium phosphate (NbPSi-0.5) composite, which is a promising solid Brønsted acid that is a potential candidate for such a high-performance catalyst. A variety of characterization results confirm that NbPSi-0.5 contains nearly pure Brønsted acid sites and has well-defined large mesopores. In addition, NbPSi-0.5 contains a similar amount of acid sites and exhibits weaker acidity than that of the highly acidic niobium phosphate and HZSM-5 zeolite. NbPSi-0.5 is quite stable and has a high activity for the dehydration of glycerol. The stability of NbPSi-0.5 is about three times higher than that of the reported catalyst. The significantly enhanced catalytic performance of NbPSi-0.5 can be attributed to 1) nearly pure Brønsted acidity, which suppresses side reactions that lead to coke formation; 2) a significant reduction of pore blocking due to the mesopores; and 3) a decrease in the amount and oxidation temperature of coke.

Highly dispersed chromium oxide catalysts supported on mesoporous silica (Cr-MSU-x) were prepared via a (N0Mn+)I0 pathway with the goal of achieving the high performance oxidative dehydrogenation of propane (ODHP) reaction. The resulting materials exhibited a mesopore structure resembling 3D wormhole-like holes, as characterized by N2 adsorption–desorption isotherms and HR-TEM. Catalytic experimental results revealed that the catalyst with a 0.028 Cr/Si molar ratio showed the highest catalytic activity among the catalysts studied. Two types of chromium species, isolated Cr(VI) and polymeric Cr(VI) species, were observed, as evidenced by H2-temperature-programmed reduction. They were designated as “hard Cr(VI)” and “soft Cr(VI)” sites, respectively. The initial composition of the soft Cr(VI) in the total Cr(VI) is a major determinant factor in the ODHP performance.

A facile and efficient approach to prepare hierarchically and radially mesoporous nano-catalysts with tunable acidic properties has been successfully developed. The nanospheres show excellent catalytic performance for the acid catalysed reactions, i.e. cracking of 1,3,5-triisopropylbenzene and hydrolysis of sucrose.