Tungsten containing materials as heterogeneous catalysts for green catalytic oxidation process

Wei-Lin Dai, Jing Ding, Quanjing Zhu, Ruihua Gao and Xinli Yang

DOI: 10.1039/9781782626855-00001

This chapter provides a comprehensive description of the recent advances in the field of tungsten-containing heterogeneous catalysts for green catalytic oxidation processes. This chapter contains three sections. The first exhibits the advances in the pristine tungsten-based catalysts for the green catalytic oxidation process. The second highlights various green catalytic oxidation reactions with tungsten-based catalysts supported on different carriers. The third illustrates the existing problems and outlook for the tungsten-based catalysts applied in the green catalytic oxidation reactions. All these contributions provide a proper guide and overview to tungsten-based catalysts for the sake of the better development of highly efficient green oxidation catalytic systems.

1 Introduction

"Green Chemistry" is now a central issue in both academia and industry due to global contamination and other environmental and health risks of chemicals. Oxidation is a core technology for converting petroleum-based materials to useful chemicals of a higher oxidation state. However, the traditional methods of oxidation always require the use of stoichiometric levels of oxidant such as chromates, permanganates and periodates, which could result in complex heat management needs and by-products that are harmful to the environment. As the increasing emerge of the environmental issue, searching for a green synthesis method of the catalysts and further for an environmentally friendly process of the catalytic oxidation are urgently needed to meet the challenging environmental demands and industrialization requirements. Nowadays, a clean and environmentally friendly process using environmental benign oxidants such as air, oxygen or hydrogen peroxide are preferred.

In recent years, there has been a growing interest in tungsten-based catalyst due to their properties and wide potential applications. This kind of materials exhibits unique acidity that improves the activity and selectivity, chemical and thermal stability and environmental protection, thus being regarded as a kind of promising catalyst owing to its versatile application, including the metathesis and isomerization of alkenes, selective oxidation of unsaturated compounds, hydrodesulfurization and hydrocracking of heavy fractions in petroleum chemistry,' and de-hydrogenation of alcohols. Moreover, the tungsten-based catalyst can be applied to the photocatalytic oxidation reaction, especially tungsten trioxide. Tungsten trioxide, with a band gap between 2.4 and 2.8 eV, is a visible light response catalyst with stability in acidic reaction conditions. The deeply positive level of the valence band (VB) makes it suitable for achieving the efficient oxidative decomposition of the organic compounds under solar or visible irradiation. In addition, tungsten-based catalysts also have been widely used in the field of electrocatalysis. For instance, tungsten trioxide, dependent on its own special electrochemical properties, can be used as an anode catalyst for hydrogen oxidation in proton exchange membrane fuel cells (PEMFCs), promoting the development of PEMFCs.

In this chapter, we aim to provide a comprehensive description of the recent advances in the field of tungsten-containing heterogeneous catalyst for green catalytic oxidation process. Though significant advances have been achieved in the development of the tungsten-containing heterogeneous catalyst in green catalytic oxidation process, there is rarely relevant review focusing on the aspect. Hence, this is our main driving force to contribute to the fundamental exemplifications in this field. This review collects more than 90 literatures and consists of three sections. The first part exhibits the advances in the pristine tungsten-based catalysts for the green catalytic oxidation process; the second one highlights various green catalytic oxidation reactions with tungsten-based catalysts supported on different carriers; the last one illustrates the existing problems and outlook for the tungsten-based catalysts applied to the green catalytic oxidation reactions. Herein, we sincerely wish to give colleagues a proper guide and overview to tungsten-based catalysts for the sake of the better development of highly efficient green oxidation catalytic systems.

2 Pristine W-based catalyst for green catalytic oxidation

Pristine tungsten-based catalyst mainly includes tungsten trioxide, tungstic acid, tungsten carbide, etc. Recently, a great deal of research based on pristine tungsten-based catalysts was focused on various green catalytic oxidation reactions, which exhibited excellent catalytic performance and chemical stability.

2.1 Tungsten trioxide catalyst for green catalytic oxidation

Tungsten trioxide (WO) is an important rare earth oxide and can be used in the field of gas sensors, catalysis, electrochemistry and photo-catalysis because of its unique gasochromic, acidity, electrochromic and photochromic properties. Tungsten trioxide, a very efficient catalyst for various acid catalyzed reactions due to its solid acidic and redox properties, is applied to some oxidation reactions, such as the selective oxidation of alcohols or aldehydes and the epoxidation of alkenes. Su et al. synthesized hexagonal single crystal WO nanorods with the aid of p-aminobenzoic acid through a facile hydrothermal method. The catalyst showed good performance for oxidation of cyclohexene to adipic acid compared to commercial WO. Meanwhile, WO3, with a band gap between 2.4 and 2.8 eV, is a visible light response catalyst with stability under acidic conditions, which makes it a suitable choice for the photocatalytic oxidation of organic pollutants under solar irradiation. The possible photocatalytic oxidation process using...