Yang Sik Yun

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.

Effect of nickel on catalytic behaviour of bimetallic Cu–Ni catalyst supported on mesoporous alumina for the hydrogenolysis of glycerol to 1,2-propanediol

The catalytic conversion of glycerol to 1,2-propanediol by hydrogenolysis has potential use in the commercial biomass industry. However, the high hydrogen pressure required for the reaction is a major drawback. To overcome this limitation, in this study, we added nickel metal to a copper-based catalyst for both supplying hydrogen via aqueous-phase reforming (APR) of glycerol and improving selectivity for 1,2-propanediol in hydrogenolysis. The bimetallic Cu–Ni catalyst supported on mesoporous alumina (MA) was prepared by a sol–gel method. The prepared Cu–Ni catalyst contains ordered mesopores with high surface area and well-dispersed active sites, as confirmed by BET, TEM, XRD, and TPR. The 9Cu–1Ni/MA (molar ratio of copper to nickel: 9 : 1) catalyst showed the highest catalytic performance among the various xCu–yNi/MA catalysts in a low pressure of H2. The XPS results showed that the surface ratio of Ni to (Cu + Ni) and Cu0/(Cu0 + Cu2+) is closely related to catalytic performance, selectivity and yield. The effect of nickel on the hydrogen production was experimentally proven by the time-on-stream tests over monometallic (Cu) and bimetallic (Cu–Ni) catalysts in the absence of hydrogen. The optimum value of the ratio of Ni to Cu is varied with the conditions in the presence of H2. The reaction mechanism was proposed for the Cu–Ni bimetallic catalysts for hydrogenolysis with APR of glycerol.

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.

Effects of Catalyst Pore Structure and Acid Properties on the Dehydration of Glycerol

Hierarchical porous catalysts have recently attracted increasing interest because of the enhanced accessibility to active sites on such materials. In this context, previously reported hierarchically mesoporous ASN and ASPN materials are evaluated by applying them to the dehydration of glycerol, and demonstrate excellent catalytic performance. In addition, a comprehensive understanding of the effects of pore structures and the acid properties on the reaction through comparative studies with microporous HZSM-5 and mesoporous AlMCM-41 is provided.

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 ).