Structure and acid catalysis of mesoporous Nb2O 5·n H2O

Kiyotaka Nakajima; Tsuyoshi Fukui; Hideki Kato; Masaaki Kitano; Junko N. Kondo; Shigenobu Hayashi; Michikazu Hara

doi:10.1021/cm100391q

Structure and acid catalysis of mesoporous Nb₂O ₅·n H₂O

Kiyotaka Nakajima, Tsuyoshi Fukui, Hideki Kato, Masaaki Kitano, Junko N. Kondo, Shigenobu Hayashi, Michikazu Hara

IMRAM - Division of Inorganic Material Research

Research output: Contribution to journal › Article › peer-review

83 Citations (Scopus)

Abstract

Mesoporous Nb₂O₅nH₂O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250-350 m² g ^-1 and pore volumes of 0.2-0.4 mL g^-1, which are larger than that of bulk Nb₂O₅·nH₂O. Fourier transform-infrared (FT-IR) analysis using CO and pyridine as basic probe molecules indicated no significant differences in the acid strength of the Lewis and BrØnsted acid sites among mesoporous, supermicroporous, and bulk Nb₂O₅·nH₂O. Mesoporous Nb ₂O₅·nH₂O exhibits much higher catalytic activity for the hydrolysis of cellobiose than supermicroporous and bulk ·nH₂O. However, no significant difference was observed between the activity of bulk and mesoporous Nb₂O₅·nH ₂O samples for Friedel-Crafts alkylation. The results suggest that mesopores consisting of hydrophilic niobium oxide are advantageous for hydrophilic reactions, but not hydrophobic reactions.

Original language	English
Pages (from-to)	3332-3339
Number of pages	8
Journal	Chemistry of Materials
Volume	22
Issue number	11
DOIs	https://doi.org/10.1021/cm100391q
Publication status	Published - 2010 Jun 8

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title = "Structure and acid catalysis of mesoporous Nb2O 5·n H2O",

abstract = "Mesoporous Nb2O5nH2O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250-350 m2 g -1 and pore volumes of 0.2-0.4 mL g-1, which are larger than that of bulk Nb2O5·nH2O. Fourier transform-infrared (FT-IR) analysis using CO and pyridine as basic probe molecules indicated no significant differences in the acid strength of the Lewis and Br{\O}nsted acid sites among mesoporous, supermicroporous, and bulk Nb2O5·nH2O. Mesoporous Nb 2O5·nH2O exhibits much higher catalytic activity for the hydrolysis of cellobiose than supermicroporous and bulk ·nH2O. However, no significant difference was observed between the activity of bulk and mesoporous Nb2O5·nH 2O samples for Friedel-Crafts alkylation. The results suggest that mesopores consisting of hydrophilic niobium oxide are advantageous for hydrophilic reactions, but not hydrophobic reactions.",

author = "Kiyotaka Nakajima and Tsuyoshi Fukui and Hideki Kato and Masaaki Kitano and Kondo, {Junko N.} and Shigenobu Hayashi and Michikazu Hara",

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T1 - Structure and acid catalysis of mesoporous Nb2O 5·n H2O

AU - Nakajima, Kiyotaka

AU - Fukui, Tsuyoshi

AU - Kato, Hideki

AU - Kitano, Masaaki

AU - Kondo, Junko N.

AU - Hayashi, Shigenobu

AU - Hara, Michikazu

PY - 2010/6/8

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N2 - Mesoporous Nb2O5nH2O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250-350 m2 g -1 and pore volumes of 0.2-0.4 mL g-1, which are larger than that of bulk Nb2O5·nH2O. Fourier transform-infrared (FT-IR) analysis using CO and pyridine as basic probe molecules indicated no significant differences in the acid strength of the Lewis and BrØnsted acid sites among mesoporous, supermicroporous, and bulk Nb2O5·nH2O. Mesoporous Nb 2O5·nH2O exhibits much higher catalytic activity for the hydrolysis of cellobiose than supermicroporous and bulk ·nH2O. However, no significant difference was observed between the activity of bulk and mesoporous Nb2O5·nH 2O samples for Friedel-Crafts alkylation. The results suggest that mesopores consisting of hydrophilic niobium oxide are advantageous for hydrophilic reactions, but not hydrophobic reactions.

AB - Mesoporous Nb2O5nH2O was prepared using amphiphilic block copolymers (L64, P103, and P123) that acted as structure-directing agents. The pore size in the prepared materials increased with increasing molecular weight of the block copolymer at the same weight percentage of ethylene oxide groups in the following order: P123 > P103 > L64. The obtained samples had BET surface areas of 250-350 m2 g -1 and pore volumes of 0.2-0.4 mL g-1, which are larger than that of bulk Nb2O5·nH2O. Fourier transform-infrared (FT-IR) analysis using CO and pyridine as basic probe molecules indicated no significant differences in the acid strength of the Lewis and BrØnsted acid sites among mesoporous, supermicroporous, and bulk Nb2O5·nH2O. Mesoporous Nb 2O5·nH2O exhibits much higher catalytic activity for the hydrolysis of cellobiose than supermicroporous and bulk ·nH2O. However, no significant difference was observed between the activity of bulk and mesoporous Nb2O5·nH 2O samples for Friedel-Crafts alkylation. The results suggest that mesopores consisting of hydrophilic niobium oxide are advantageous for hydrophilic reactions, but not hydrophobic reactions.

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Structure and acid catalysis of mesoporous Nb₂O ₅·n H₂O

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