green chemistry catalysis

A comprehensive birds eye view of catalysis in green chemistry. Includes descriptions of photocatalysis,zeolites and nanoparticles as efficient green catalysts.A simple and crisp presentation with minimum words and alot of figures and colors.

1. GREEN CATALYSTS

2. ZEOLITES  THE "BOILING STONE"

3. WHAT ARE ZEOLITES Zeolites, also called molecular sieves, are traditionally referred to as a family of aluminosilicate materials consisting of orderly distributed micropores in molecular dimensions. •In simpler words, they're solids with a relatively open, three-dimensional crystal structure built from the elements aluminum, oxygen, and silicon, with alkali or alkaline-Earth metals (such as sodium, potassium, and magnesium) plus water molecules trapped in the gaps between them. They have been widely used as highly efficient catalysts, adsorbents, and ion exchangers in petrochemical industries and in our daily life.

4. ZEOLITES AS GREEN CATALYST

5. BRONSTED ACID CATALYSTS

6. LEWIS ACID CATALYST

7. MULTIFUNCTIONAL CATALYST The transformation of biomass into chemicals and fuels often undergoes multistep reactions, each of which might require a distinct catalyst. Zeolite catalysts can be fine-tuned with combined active sites to allow multistep reactions occurring in a “one-pot” way.    For instance, zeolite Sn-Al-beta contains both Brønsted and Lewis acid sites because of the presence of both tetrahedral Al III  and Sn IV , respectively, which can be used for the cooperative catalysis of multistep conversion of 1,3-dihydroxyacetone into ethyl lactate . During this multistep reaction, the Brønsted Al III  acid sites accelerated the dehydration of dihydroxyacetone to form pyruvic aldehyde, and the Lewis Sn IV  acid sites catalyzed the hydride shift of pyruvic aldehyde into ethyl lactate with ethanol.

8. TiO2 Photocatalyst

9. Environmental pollution and destruction on a global scale have drawn attention to the vital need for totally new environmentally friendly, clean chemical technologies and processes, the most important challenge facing chemical scientists in the field of green chemistry. Strong contenders as environmentally harmonious catalysts are photocatalysts that operate at room temperature and in a clean manner, while applications of such safe photocatalytic systems are urgently desired for the purification of polluted water, the decomposition of offensive atmospheric odors as well as toxins, the fixation of CO2, and the decomposition of NOx and chlorofluorocarbons on a huge global scale. One of the most ideal catalytic processes is the so-called ‘artificial photosynthesis’ which has the potential to realize safe and clean chemical processes and systems with the use of limitless solar energy

10. ADVANTAGES , TiO2 is the most attractive due to its low cost  Availability  high photocatalytic reactivity  chemical stability LIMITATION TiO2 has a large bandgap with an absorption edge in UV regions shorter than 380 nm   TiO2 semiconductors  absorb only 3–4% of the solar light that reaches the Earth

11. Working semiconducting metal oxides such as TiO2, ZnO and Fe2O3 are known to act as sensitizers for light-induced redox processes due to their unique electronic structure characterized by a filled valence band and an empty conduction band  when semiconducting metal oxide absorbs a photon having an energy larger than its bandgap, an electron is promoted from the valence band to the conduction band, leaving a hole The holes in the valence band act as powerful oxidants, while the electrons in the conduction band are good reductants When the TiO2 is irradiated by UV light (l < 380 nm) in water, H+ is reduced to H2 by the photo-formed electrons, while OH is oxidized to OH  radicals by the photo-formed holes to produce O2 through several reaction steps. In this way, TiO2 can decompose water into H2 and O2  It should be noted that the irradiation of vacuum UV light (l < 165 nm) is necessary for the direct photolysis of water molecules into H2 and O2 [1–6].  On the other hand, when TiO2 is irradiated by UV light in the presence of air and reactant molecules such as organic compounds in water, the photo-formed electrons react with O2 to form O2 , while OH is  oxidized into OH q radicals. The oxygen radicals formed can easily react with the organic compounds, decomposing them into CO2 and H2O 

12. Direct Photocatalytic Decomposition of NO into N2 and O2 When the TiO2 photocatalyst is irradiated by UV light in the presence of NO in atmospheric conditions, NO is oxidized into NO2 and then further oxidized into NO3 . This NO3  species on the TiO2 surface can be removed as HNO3 by water in the form of, for example, raindrops    

13. MODIFICATION FOR TiO 2    PHOTOCATALYST A modification of the electronic properties of Ti /zeolite photocatalysts by bombarding them with high-energy metal ions led to the discovery that metal ion implantation with various transition metal ions such as V and Cr, accelerated by high electric fields, can produce a large shift in the absorption band toward visible light regions

14. NANOMATERIAL CATALYSTS

15. WHY DO WE NEED NANO-CATALYSIS ?

16. PROPERTIES OF NANOCATALYSTS

17. APPLICATIONS OF NANOCATALYSTS Biomass gasification to produce high syn gas and biomass pyrolysis for production of bio-oil Process Improvements: • Novel Al2O3 supported NiO catalyst reduces tar yield significantly and increases tar removal efficiency to 99% • Significant increase in gas yield • Lighter fractions of H2 & CO are increased in the syn gas composition while heavier fractions of CH4 & CO are reduced, thus improving syn gas quality Catalyst: Nano NiO catalyst supported on γ- Al2O3 microspheres of 3 mm size (Johnson Mathey Company, greater than 99% purity) Application: Production of biodiesel from waste cooking oil Process Improvements: • Esterification of fatty acids (FFAs) and transesterification of triglycerides to biodiesel in one pot • Solid acid nanocatalysis of Al0.9H0.3PW12O40 nanotubes with double acid sites yield 96% of biodiesel from waste cooking oil as compared to 42.6% with conventional H3PW12O40 catalyst Catalyst: Aluminium dodeca-tungsto-phosphate (Al0.9H0.3PW12O40) nanotubes as solid catalysts with surface area of 278 m2/g