Green Catalysis, Volume 2

Heterogeneous Catalysis

Paul T. Anastas

• Publisher: Wiley-VCH
• Year: 2014
• Print ISBN: 9783527324972
• eBook ISBN: 9783527688630
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Environmental Science

The shift towards being as environmentally-friendly as possible has resulted in the need for this important volume on heterogeneous catalysis. Edited by the father and pioneer of Green Chemistry, Professor Paul Anastas, and by the renowned chemist, Professor Robert Crabtree, this volume covers many different aspects, from industrial applications to the latest research straight from the laboratory. It explains the fundamentals and makes use of everyday examples to elucidate this vitally important field.

Chapter 1
Zeolites in Catalysis

Stephen H. Brown

1.1 Introduction

Acid catalysis as a modern science is less than 150 years old. From its inception, acid catalysis has been explored as a means of producing fuels, lubes and petrochemicals. Ordinary homogeneous acids, both inorganic and organic, never proved industrially useful at temperatures much above 150 °C. The first reports of aluminosilicate solid acid catalysts involved the use of clays after the turn of the century. The inspiration for the first commercial synthetic aluminosilicate catalysts came from work done co precipitating silicon and aluminum salts during WWI by a Sun Oil chemist [1]. The Br

nsted acid site in these materials is most often represented as in Scheme 1.1. Useful features of this novel type of acid versus homogeneous liquid acids were their high temperature stability, moderate acidity (roughly equivalent to a 50% sulfuric acid solution), solid and non-corrosive character and regenerability by air oxidation. These features enabled acid catalyzed reactions of chemicals to be contemplated at a greatly extended range of temperatures (up to 600 °C) and metallurgies.

Scheme 1.1 The Br

nsted acid site of an aluminosilicate.

The first embodiments of many modern refining processes including heavy oil cracking, naphtha reforming and light gas oligomerization did not use catalysts [2]. As soon as these thermal processes commercialized, exploration of the use of solid acid catalysts ensued naturally.

Because of the key role played in the development of the automotive industry, heavy oil cracking to gasoline provided a focal point for the early development of heterogeneous acid catalysis. Temperatures above 400 °C and pressures below 3 atmospheres are thermodynamically favorable for the conversion of heavy oils to light hydrocarbons rich in olefins. Acceptable heavy oil cracking rates are achieved without a catalyst at temperatures above 600 °C. This was the basis of the thermal cracking process. Thermal cracking produces high yields of methane and aromatic hydrocarbons. The goal of researchers was to find a catalyst that could crack heavy hydrocarbons selectively to gasoline with only minimal formation of gases with molecular weights of less than 30. Due to thermodynamic constraints, the catalyst had to be effective at a temperature above 400 °C. In order to avoid unselective thermal cracking, the catalyst had to be effective below 550 °C.

The discovery in the early 1920s by Houdry that acid activated clays were active and selective in this temperature window was a breakthrough [2]. In the 1930s and 1940s methods were developed and commercialized to produce high surface area man-made aluminosilicates that were significantly improved catalysts. Examination of the aluminosilicate catalysts led to the understanding that the active site was a Br

nsted acid [3].

At the time of the discovery of synthetic zeolites in the early 1950s, only two classes of solid Br

nsted acids (solid phosphoric acid and aluminosilicates) were being used commercially to produce commodity fuels or petrochemicals [4]. The commercialization of silica-rich synthetic zeolites in their hydrogen form represented a breakthrough for scientists and organizations interested in the production of fuels, lubes and petrochemicals at temperatures above 200 °C. Like amorphous aluminosilicates, zeolite Br

nsted acid sites are active and stable up to 600 °C. Shortly after Union Carbide's discovery of synthetic zeolites in the late 1940s, Mobil Oil researchers in catalytic cracking of heavy oil investigated zeolites as potential catalysts [5]. The zeolite known as faujasite (FAU) was found to be three to five orders of magnitude more active than amorphous aluminosilicates. Unmodified, FAU was too active to be useful. When the activity of FAU was tuned by ion exchange with rare earth cations and/or by reducing aluminum content, it was found to have a dramatically different selectivity to cracked products. Optimized samples of FAU zeolites produced almost 5% less C₂-gases and coke and increased gasoline yields by more than 10 wt%. Over the course of the past 50 years, evolving heavy oil cracking catalysts and hardware have been continuously decreasing coke and C₂-gas yields while increasing the yield of gasoline.

The commercialization of zeolite catalysts for heavy oil cracking unleashed the creative abilities of every organization interested in producing fuels and petrochemicals using acid catalysts between 250 and 600 °C. Close to 23 processes have been commercialized (Table 1.1). About two-thirds of the processes had no real precedence using homogeneous acids. The other third involved displacement of homogeneous and amorphous acid cataly...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• About the Editors
• List of Contributors
• Chapter 1: Zeolites in Catalysis
• Chapter 2: Sol–Gel Sulfonic Acid Silicas as Catalysts
• Chapter 3: Applications of Environmentally Friendly TiO2 Photocatalysts in Green Chemistry: Environmental Purification and Clean Energy Production Under Solar Light Irradiation
• Chapter 4: Nanoparticles in Green Catalysis
• Chapter 5: ‘Heterogreeneous Chemistry’
• Chapter 6: Single-Site Heterogeneous Catalysts via Surface-Bound Organometallic and Inorganic Complexes
• Chapter 7: Sustainable Heterogeneous Acid Catalysis by Heteropoly Acids
• Chapter 8: The Kinetics of TiO2-based Solar Cells Sensitized by Metal Complexes
• Chapter 9: Automotive Emission Control: Past, Present and Future
• Chapter 10: Heterogeneous Catalysis for Hydrogen Production
• Chapter 11: High-Throughput Screening of Catalyst Libraries for Emissions Control
• Chapter 12: Catalytic Conversion of High-Moisture Biomass to Synthetic Natural Gas in Supercritical Water
• Index
• End User License Agreement