## 4 Applications of Zeolites in Catalysis, Bioprocesses, and Environmental Remediation  
### Production of Light Olefins  
Light olefins are important substances that are building blocks of derivative substances from the petroleum industry, such as polyethylene and polypropylene [247]. The main compounds in the light olefin family are ethylene, propylene and butene, which have been of great importance for the petrochemical industry. The global demand for these products is higher than other petrochemical products. As an example, the demand for propylene was 82 million tons in 2010 and is expected to reach 165 million tons by 2030 [248]. For this production, fractions of gasoline and gas are used and the main process is the catalytic cracking of vacuum gas oil. An example is the propylene production that accounts for 81% of the yield (50% from steam cracking and 31% from FCC). The nature of feedstock used influences this quantity: heavy feed produces high propylene content, while lighter feed is produces low propylene content. Alternative feedstocks such as natural gas, coal, and biomass (a carbon-neutral feedstock) can be used, as well as other related feedstocks, such as vegetable oils in pyrolysis and thermal cracking. The bio-oil obtained from woodworking (sawdust) pyrolysis, a lignocellulosic biomass, is useful for light olefin production in spite of some difficulties faced, such as the coking property. The use of Fischer-Tropsch synthesis may be helpful for olefin production from synthesis gas, a better process to transform biomass, but nonetheless there is high greenhouse gas generation in the form of methane and carbon dioxide. Another approach is the MTO (methanol to olefins) reaction [247; 248; 249]. Crude oil is another feedstock highlighted for light olefin production [250]. The fluid catalytic cracking (FCC) method is the main catalytic conversion process used with lower CO\({}_{2}\) generation and higher energy economy, using much lower temperature in operation than steam cracking. The innovation in process development is reached because of high capacities of the cracking unit; therefore, the redesign of the unit improves the olefin production. Two of these innovations are the catalytic pyrolysis process (CPP) and deep catalytic cracking process (DCC) [251]. The increase in light olefin production is achieved by reaching severe conditions in the FCC process with higher reaction temperature or ratio catalyst/oil. This leads to excessive dry-gas (C\({}_{1}\) and C\({}_{2}\)) production and higher hydrogen transfer activity. The severity of process conditions and the adequate design of catalysts have fundamental roles in optimal light olefin generation. FCC catalysts are responsible for decreasing the activation energy for breaking the C-C bonds while the temperature decreases. The adequate selectivity for desired products is a function of the catalyst, where the coke may be removed by regeneration or decoking. The main types of catalysts used are acids, basics and transition metal oxides. Proton donor catalysts such as zeolites are solid acid catalysts and highly active in cracking hydrocarbons [247; 248; 249; 250; 251]. The conversion of syngas into light olefins (STO) has been used with catalytic support of zeolitic structures. The direct conversion was made using Fisher-Tropsch (FT) catalysts, because the introduction of a second zeolite phase to the conventional FT catalysts may optimize the hydrocarbon distribution [252]. The use of bifunctional catalysts such as Zr/Cr oxide and SAPO-3 zeolite allows the direct synthesis of light olefins from syngas with 80% selectivity [253]. The conversion of CO or CO\({}_{2}\) to light olefins by SAPO zeolites is reported in use of other bifunctional systems, such as ZnZr/SAPO-34, ZnAl/SAPO-34, MnO\({}_{x}\)/SAPO-34 and InZr/SAPO-34 [254]. The use of ZSM-5 zeolite, with strong acidity, in reaction with STO results in the initial formation of paraffins or aromatics [255].