Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

Summary

A protocol for the synthesis of HNbWO₆, HNbMoO₆, HTaWO₆ solid acid nanosheet modified Pt/CNTs is presented.

Abstract

We herein present a method for the synthesis of HNbWO₆, HNbMoO₆, HTaWO₆ solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO₆/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO₆/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH₃-temperature programmed desorption. The study revealed that HNbWO₆ nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs < Pt/5HNbWO₆/CNTs < Pt/20HNbMoO₆/CNTs < Pt/20HNbWO₆/CNTs < Pt/20HTaWO₆/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO₆ catalyst has been investigated.

Introduction

Many industrial processes for the manufacture of chemicals involve the use of aqueous inorganic acid. One typical example is the conventional H₂SO₄ process for the hydration of cyclohexane to produce cyclohexanol. The process involves a biphasic system, with the cyclohexane being in the organic phase and the cyclohexanol product being in the acidic aqueous phase, thus making the separation process by simple distillation difficult. Apart from difficulty in separation and recovery, inorganic acid is also highly toxic and corrosive to equipment. Sometimes, the use of inorganic acid generates byproducts that will lower the product yield and must be a....

Protocol

CAUTION: For the proper handling methods, properties and toxicities of the chemicals described in this paper, refer to the relevant material safety data sheets (MSDS). Some of the chemicals used are toxic and carcinogenic and special care must be taken. Nanomaterials may potentially pose safety hazards and health effects. Inhalation and skin contact should be avoided. Safety precautions must be exercised, such as performing the catalyst synthesis in the fume hood and catalyst performance evaluation with autoclave reactors. Personal protective equipment must be worn.

1. Pretreatment of CNTs¹³

1. Immerse 1.0 g....

Results

X-ray diffraction patterns (XRD) have been studied for the precursor LiNbWO₆ and the corresponding proton-exchanged catalyst sample HNbWO₆ to determine the phase (Figure 1 and Figure 2). NH₃-temperature programmed desorption (NH₃-TPD) was used to probe the surface acidity of the catalyst samples (Figure 3). Scanning electron microscopy (SEM) with X-ray microanalysis and.......

Discussion

Pretreatment of CNTs with nitric acid does increase the specific surface area (S_BET) significantly. Raw CNTs have a specific surface area of 103 m²/g while after treatment, the surface area was increased to 134 m²/g. Therefore, such pretreatment to create defects on the CNT surface will have a positive effect on the specific surface area on the catalysts after solid acid modification and platinum particle impregnation. Since the surface area will decrease after incorporation of nanosheets.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Carbon nanotubes (multi-walled)	Sigma Aldrich	724769
Nitric acid (65%)	Sigma Aldrich	V000191
sulphuric acid (98%)	MERCK	100748
Lithium carbonate (>99%)	Aladdin	L196236
Niobium pentaoxide (99.95%)	Aladdin	N108413
Tungsten trioxide (99.8%)	Aladdin	T103857
Molybdenum trioxide (99.5%)	Aladdin	M104355
Tantalum oxide (99.5%)	Aladdin	T104746
Chloroplatinic acid hexahydrate, ≥37.50% Pt basis	Sigma Aldrich	206083
tetra (n-butylammonium) hydroxide 30-hydrate	Aladdin	D117227
Diphenyl ether, 98%	Aladdin	D110644
2-Bromoacetophenone,98%	Aladdin	B103328
Diethyl ether,99.5%	Sinopharm	10009318
n-Decane,98%	Aladdin	D105231
n-Dodecane,99%	Aladdin	D119697
Autoclave Reactor			CJF-0.05—0.1L (Dalian Tongda Equipment Technology Development Co., Ltd)
Tube furnace			SK2-1-10/12 (Luoyang Huaxulier Electric Stove Co., Ltd)