Catalysis

Catalysis is a key component of the chemical process for almost every important industrial reaction. It is used in environmental controls to destroy CO and VOC's (as it does in the catalytic converter in an automobile), and is essential to the production of specific chemical commodities (high-octane gasoline being one of the more valuable ones). Catalysts are used extensively in refining and chemical processing, and in the gasification process they are used in the Water Gas Shift (WGS) reaction to produce hydrogen from a mixture of CO and H2O. While hydrogen is widely used in the processing industry, there is little application for it beyond refining and petrochemicals. There is no distribution network, and its low energy density makes it an enormous challenge to substitute directly as a fuel for the transport sector. For hydrogen, this has been, and remains, a major barrier.

In the 1920s it was discovered that several catalysts (Iron and Cobalt) could combine CO and H2 to produce long chain hydrocarbons into synthetic oil. Substantially paraffin in structure, they could readily substitute for the straight chain hydrocarbons needed in the diesel reciprocating engine. In catalysis, particle size, uniformity, and dispersion are key factors. The greater the surface area is, the more reactive the catalyst, assuming the material shows catalytic activity. Combining catalyst chemistry with new nanostructures has the potential to yield significant improvements in catalyst reaction rates. In one novel process, the electronic properties of iron can be controlled by confining metallic nanoparticles inside carbon nanotubes. This alters the redox properties of the particles and can enhance their effectiveness as catalysts [20]. There is also interest in whether hydrogen could be produced at much less severe conditions, possibly even using photochemically driven reaction pathways [21]. Under such a scenario, it may be possible to realize much more widespread production of hydrogen from an energy source that is genuinely abundant—sunshine.

Particle size plays a very unusual role regarding the catalytic properties of gold. In its bulk form, gold exhibits little or no catalytic properties—that lack of reactivity and its price have kept gold at a distance from catalytic processes. On the nano-scale, it behaves differently. Researchers at Northwestern have shown that gold nanopar-ticles can accelerate the oxidation of carbon monoxide at room temperature [22]. In most industrial applications, gas temperatures are typically maintained above 500°C to ensure complete oxidation of CO to CO2. Controlling the morphology of the surface to affect a specific outcome is a frontier in catalysis that seems to be continually renewed. One may find applications in energy storage, energy conversion, and pollution control. Because the volumes needed to coat a surface with nano-particles would be very small, the cost impact of using even a rate mineral as a catalyst is greatly reduced.

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