Zeolite Catalysts – What is Zeolite and Their Examples?
The word “zeolite” is used to describe a mineral that has catalytic properties. The mineral’s use can be very beneficial for many industries. These include petrochemical, water treatment, food processing, and medical applications. This article will explore the properties and potential applications of zeolites.
Natural Zeolites
Natural zeolites are crystalline aluminosilicates made from oxygen, silicon, and aluminum. They are found naturally in rocks and sediments. Zeolites are also manufactured. However, they are usually chemically modified.
Zeolites are typically formed through the crystallization of silica-alumina gel, which has been added to organic templates and alkalis. The resultant zeolites are less stable than their natural counterparts. Various methods are used for their synthesis, including thermal and hydrothermal processes.
Several studies have been done to understand the behavior of natural zeolites. These findings have revealed that they are cationic exchangers. This property makes them useful in water softening applications, as well as in the treatment of wastewater. As a result, many commercial washing powders contain substantial amounts of zeolites. Moreover, they exhibit excellent selectivity for different cations at low temperatures.
One of the primary pollutants in wastewater is ammonium. Ammonium binds to zeolites through two parallel processes. For this reason, further research should focus on improving the chemical stability of modified zeolites. In addition, further industrial research should also concentrate on exploring the surface-binding properties of zeolites.
In addition to their aluminosilicate framework, zeolites can also be modified to capture anions. Some of these changes include the addition of a quaternary ammonium cation or positively charged oxi-hydroxides.
Catalytic Properties
Zeolites are one of the most effective catalysts for various chemical processes. They are a group of microporous materials with bronsted solid acid sites. These pores allow small molecules to diffuse through and trap larger ones. The zeolite framework also exhibits shape selectivity.
Zeolites are used in industrial applications as water softeners, depleting radioactive cations from liquid nuclear waste, and removing toxic heavy metal ions from groundwaters. A zeolite can be exchanged with positively-charged ions such as H+ or Na+ in an aqueous solution.
Typical zeolites contain a Si/Al ratio of 30. This makes them less acidic than a zeolite with a higher Si/Al. Some zeolites, such as those dedicated to NaOH or TPAOH, display good acid properties and mesoporosity.
Among the silica-based binders, alumina is the most widely used. Its low cost and thermal stability make it suitable for use as a binder. Besides, g-Alumina has a crystalline framework and moderate Lewis acidity. In addition, what can modify it with meso- or macropores?
There are nearly twenty zeolite structures currently in commercial use. Many researchers are focusing on zeolites’ costs, simplicity, and textural properties. Moreover, they are applying efforts to minimize the textural properties of zeolites.
Several factors determine the acidity of zeolites. Most studies on zeolites’ acidity have been done using a method called TPD-NH3. Pyridine was adsorbed on a zeolite to study its acidity during this process. Various data were collected, including frequency shifts of OH bands interacting with CO, stretching frequency of CO molecules, and acid strength of hydroxyl groups.
Applications
Zeolite applications are found in a variety of fields. These include air pollution remediation, water purification, biomass conversion, and CO2 capture.
One of the most apparent advantages of zeolites is their superior adsorption capability. They have been used in the oil refining industry for several decades. In addition, they have also been employed in a wide range of medical and biomedical applications.
For example, they are bactericidal agents in dental and MRI contrast agents. They also have been found to improve the bioavailability of drugs in the gastrointestinal tract. Moreover, they are effective in controlling bone resorption.
In addition, zeolite is a promising material for controlled drug delivery. It can also be used for oral delivery of pharmaceuticals targeting intestinal worms or gastric cancer. Besides, they have the potential to improve the immunity of farm animals.
Zeolites can be formed from kaolin, feldspar, or bauxite. Zeolite has also been functionalized with metal oxides and transition metals. This can lead to producing new types of zeolite highly desirable for superior catalytic and adsorption performance.
The synthesis of zeolites has led to expanding exploitation in biomedical research. However, their widespread application could be improved. Despite this, their theoretical analysis is essential for each of the applications.
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