Research on the application of catalysts in environmental protection(2)

2.4 Types of environmental catalysts and current status of utilization

There are various environmental problems on the earth, and the problems that we need to solve urgently are: greenhouse effect, ozone layer depletion, expansion of acid rain, emission of heavy metals and other environmental pollutants, reduction of tropical rainforest and soil desertification. 

The first three of these problems are caused by chemical substances that are emitted into the atmosphere. For example, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are related to the greenhouse effect, Freon and N2O destroy the ozone layer, and sulfur dioxide (SO2) and NOX are the main factors in the formation of acid rain and photochemical smog, and the solution to remove or reduce these pollutants is mainly through chemical methods. Because of the low amount of reactants involved in the emission process, the reaction temperature is either too high or too low, and the contact time between the reactants and the catalyst is particularly short, environmental protection catalysts require higher activity, selectivity and durability than other catalysts for chemical reactions, and are more difficult to produce.

2.5 New environmental catalysts

Silicate materials Natural clays such as montmorillonite have a molecular sieve-like structure and are good adsorbents for catalyst carriers and for treating heavy metal ions in wastewater. It is widely used as a carrier for environmental protection catalysts such as automobile exhaust gas purification, flue gas desulfurization, denitrification and catalytic combustion of organic waste gas.

TiO2 is an N-type semiconductor with good photosensitive conductivity, often used as a catalyst carrier. Now TiO2 is widely used as photocatalyst and electrode catalyst, coated with active TiO2 self-cleaning glass, tiles, furniture, curtain cloth, in the sun and light irradiation automatically catalyze and purify the air in the room.

The biocatalytic process is usually based on non-toxic and harmless biological materials as raw materials, which can be reacted at room temperature and pressure, and the process is simple. Biocatalyst is an ideal green catalyst because of its high conversion rate, high specificity, low by-products and repeated use.

Room temperature ionic liquids can be used both as acid catalysts and as a green solvent. With the advantages of easy production, low toxicity, low cost, non-combustibility and adjustable performance, it is predicted to be an environmentally friendly catalyst with the potential to cause a chemical industrial revolution and good prospects for industrial application.