**2. Short-chain hydrocarbons in air**

The release of pollutants and contaminants in nature associate with the industrial revolution since the 1800th. Since that, humans were able to release huge amounts of pollutants into air, water, and soil. As the population increases rapidly, the industrial activities have to grow at the same—or even more—rate. As a result, nature is badly affected by releasing such contaminants and severe problems were developing in animals, plants, water, and of course in humans. Few reasons have been identified as main sources of increasing pollutants and contaminations in air, water, and soil. Those reasons include the not-well-planned industrial growth, the continuation of using the old fashion technologies in several simple and manual industries, the presence of huge numbers of small-scale industries with poor facilities, and more importantly, insufficient waste disposal. Scientists realized the fact of fighting/controlling contaminations since 1950s when they realized that contaminations can be a real threat to the nature. Since that, many attempts were reported to control the environmental problems, which have been caused due to the industrial contaminations such as controlling the pollutants in air and in drinking water [2].

#### *Introductory Chapter: Photocatalysis – Principles, Opportunities, and Applications DOI:http://dx.doi.org/10.5772/intechopen.110420*

The hydrocarbons with a short-chain skeleton, either saturated or unsaturated (also called C1-C3) are representing the threats to the earth. C1-C3 VOC can be released into air from different sources, such as oil plants, during their production and/or in the chemical industries when they are used in them. C1-C3 VOC can be also released as a result of combustion processes, such as waste burning. Moreover, the C1-C3 VOC can also be found in the exhaust fumes of different vehicles, moreover, they can be also found as a result of natural gas combustion in gas power plants. The importance of catalysis for eliminating/reducing human effects on the environment was established several years ago. Generally, almost 95% of the environmental pollution control is carried out by using catalysts. Catalysis considers the major key technology for controlling gas emissions in the different types/scale industries. Catalysis can control gas emissions in two ways, first: by minimizing the number of waste by-products, and second: by treating the gases emitted during the industrial activities. The famous example of automotive catalytic converter is a perfect example of controlling the gas emission by catalysis.

The catalytic reaction of the saturated C1-C3 VOC (e.g. methane, ethane, and propane) is not easy because of the high stability of these compounds. The activation energy needed to oxidize these compounds is high to activate the very stable C-H bonds, while the unsaturated hydrocarbons (e.g. ethylene and propylene) are easy to be oxidized and over oxidized to produce CO2. Conventional catalysis techniques such as full oxidation by using noble metals (Au, Pt, Rh, or Pd) or the metal oxides of transition elements and doped metal oxides are effective to degrade C1-C3 VOC at elevated temperature (sometimes 800°C). The needed high temperature in addition to the ease poisoning of the catalysts makes the commercialization of such process not feasible because of the extremely high cost of the overall process [3].
