Tae Yong Kim

A Mesoporous Carbon‐Supported Pt Nanocatalyst for the Conversion of Lignocellulose to Sugar Alcohols

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.

A tailored catalyst for the sustainable conversion of glycerol to acrolein: mechanistic aspect of sequential dehydration.

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.

Preparation and characterization of mesoporous Zr-WOx/SiO2 catalysts for the esterification of 1-butanol with acetic acid

Zr-WOx clusters on WOx/ZrO2 catalysts are known to be active sites for the acid catalyzed reactions, such as dehydration of alcohols and alkane isomerization reactions. However, synthetic methods for producing high density of Zr-WOx clusters with high surface areas are not currently available. Herein, a facile method for preparing mesoporous Zr-WOx/SiO2 is proposed and the effect of Zr/W ratio on its structure and acidity was examined. Results showed that the sequential hydrolysis of zirconium and tungsten via soft-templating resulted in the formation of Zr-WOx clusters with uniform mesopore structures and a high acidity. The prepared Zr-WOx/SiO2 was characterized by N2 physisorption, XRD, TEM, XPS, UV-Vis spectroscopy, NH3-TPD and in situ FTIR. Catalytic performance for the esterification of 1-butanol with acetic acid was evaluated. The materials had a high surface area of over 500 m2 g−1 and ordered cylindrical pores with a uniform size of ca. 5 nm. Below a Zr/W ratio of ∼0.5, the zirconium was primarily associated with tungstate rather than SiO2, which indicates the formation of Zr-WOx clusters. The highest density of Zr-WOx clusters was obtained at a Zr/W ratio of 0.3 with a strong Bronsted acidity. Consequently, Zr-WOx/SiO2, as a Zr/W ratio of 0.3, exhibited the highest activity with a significantly improved performance compared to HZSM-5 and WOx/ZrO2 catalysts.

Selective production of 1,3-butadiene using glucose fermentation liquor

The production of 2,3-butanediol from glucose fermentation products and its subsequent esterification and conversion to 1,3-butadiene is reported. The addition of formic acid and acetic acid (C1–C2 acids) to the esterification reaction mixture resulted in yields of the diesters of 70% and 85%, without the loss of C1–C2 acids during the reaction. In the pyrolysis step, a highly selective (94% and 82% for formic acid 2-formyloxy-1-methyl-propyl ester and acetic acid 2-acetoxy-1-methyl-propyl ester, respectively) C–O cleavage to 1,3-butadiene over diesters was achieved without a catalyst. In the case of acetic acid, 100% was recovered, whereas in the case of formic acid, only 20% was recovered. Based on these results, it can be concluded that using glucose fermentation liquor as the starting material with external addition of acetic acid (2,3-butanediol:formic acid:acetic acid = 1:0.5:2.5), 70% yield of 1,3-butadiene can be achieved where the loss of formic acid is compensated by the acid in the starting material.

Selective Activation of Methane on Single-Atom Catalyst of Rhodium Dispersed on Zirconia for Direct Conversion

Direct methane conversion into value-added products has become increasingly important. Because of inertness of methane, cleaving the first C-H bond has been very difficult, requiring high reaction temperature on the heterogeneous catalysts. Once the first C-H bond becomes activated, the remaining C-H bonds are successively dissociated on the metal surface, hindering the direct methane conversion into chemicals. Here, a single-atom Rh catalyst dispersed on ZrO2 surface has been synthesized and used for selective activation of methane. The Rh single atomic nature was confirmed by extended X-ray fine structure analysis, electron microscopy images, and diffuse reflectance infrared Fourier transform spectroscopy. A model of the single-atom Rh/ZrO2 catalyst was constructed by density functional theory calculations, and it was shown that CH3 intermediates can be energetically stabilized on the single-atom catalyst. The direct conversion of methane was performed using H2O2 in the aqueous solution or using O2 in gas phase as oxidants. Whereas Rh nanoparticles produced CO2 only, the single-atom Rh catalyst produced methanol in aqueous phase or ethane in gas phase.

Understanding the Reaction Mechanism of Glycerol Hydrogenolysis over a CuCr2O4 Catalyst

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.

Effect of acid type in WOX clusters on the esterification of ethanol with acetic acid

Tungsten oxide clusters supported on silica (WOX/SiO2) with different W loading levels and the effect of acid type on the esterification of acetic acid with ethanol were examined. The catalysts were characterized using various techniques (XRD, Raman spectroscopy, NH3-TPD and FT-IR) to investigate the crystallinity and the nature of the acid sites. The change in the composition of two tungsten oxide species (polytungstate and crystalline WO3) leads to the change of Lewis acid to Brønsted acid ratio. Importantly, the ratio of the two different acid types has a substantial effect on the catalytic activity. The fraction of Lewis acid to total acid sites rapidly changed from 23% to 77% due to the presence of crystalline WO3. Where the Lewis acid sites accounted for 55% of the total acid sites, the WOX/SiO2 catalyst showed the highest catalytic activity among the prepared catalysts.

A New Energy‐Saving Catalytic System: Carbon Dioxide Activation by a Metal/Carbon Catalyst

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