Youngbo Choi

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.

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.

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.

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.