Jayeon Baek

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.

Mesoporous Siliconiobium Phosphate as a Pure Brønsted Acid Catalyst with Excellent Performance for the Dehydration of Glycerol to Acrolein

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.

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.

Promotional Effect of Ni on a CrOx Catalyst Supported on Silica in the Oxidative Dehydrogenation of Propane with CO2

As CrOx catalysts supported on the SBA‐15 support (Cr/Si) are highly active, they represent potentially promising catalysts for the oxidative dehydrogenation of propane with CO2 (ODHP). However, reduction of the active sites (Cr3+) during the reaction is known to lead to severe deactivation. The findings reported herein indicate that after the addition of 0.5 wt % Ni to 10 wt % Cr/Si (0.5 Ni‐Cr/Si), the catalytic activity was stable and the selectivity was high. Reduced CrOx was easily regenerated by the addition of Ni, as evidenced by a three‐step H2‐temperature programmed reduction analysis. In addition, ex situ XPS results revealed that Cr3+ was maintained only in the Ni‐promoted catalyst whereas Cr3+ was easily reduced to Cr2+ in the non‐promoted catalyst during the reaction. The role of the Ni added to the catalyst elucidates that Ni induces the dissociation of CO2 to CO and activated O (O*ads). Then, the generated O*ads regenerates the reduced CrOx. Consequently, the Ni‐promoted Cr/Si catalyst enhances the catalytic stability of propylene in the ODHP reaction.