How Hydrogen Deactivate Ceramic Surface Catalysis

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What is Catalysis

Catalysis is the process by which a chemical reaction among two or more elements becomes faster or slows down in the presence of an additional substance, or catalyst. Those elements which constitute the reaction, called the reagents, are consumed in the process. The catalyst is unique because though it can increase or decrease the speed at which a chemical reaction takes place; the catalyst itself does not become consumed by the reaction. Rather, once the chemical reaction is complete and the product of the reagents returns to equilibrium, the catalyst continues to remain and may perform the same function in any number of similar chemical reactions. When two chemicals come into contact with one another to produce a reaction, a specific amount of energy is required to initiate the reaction. This energy is called activation energy. The role of a catalyst is to increase or decrease the activation energy required for two chemicals to react. Promoter catalysts are substances known to increase the rate at which a chemical reaction occurs by reducing the activation energy required. By contrast, catalytic poisons are known to decrease this reaction rate by increasing the necessary activation energy between two reagents. A catalyst whose physical state (i.e., solid, liquid or gas) is different from that of the reagents is called a heterogeneous catalyst. A catalyst in the same physical state as the reagents is called a homogeneous catalyst. Sulfuric acid is an example of a simple homogeneous promoter catalyst when introduced in a reaction between starch and boiling water. Alone, the starch and boiling water react to produce sugar at a very slow rate. Sulfuric acid reduces the necessary activation energy and more quickly brings both of these into equilibrium. Enzymes are an example of catalysts in living organisms because they increase the rate at which reactions occur to produce chemicals necessary for survival.

What is Ceramic Surface Catalysts

Ceramic surface catalysts are largely heterogeneous and act upon reactions between either liquids or gases. Ceramic surface catalysts are ceramic devices constructed so that the surface area is maximized. For this reason, ceramic surface catalysts frequently appear as a grid or honeycomb when viewed straight on, with a thickness of around 2 centimeters. The surfaces of this device are covered with a chemical or metal that behaves as a catalyst in the presence of two reagents. Spread over all surfaces of the device, the catalytic material is able to catalyze more atoms effectively at a time during a reaction. In this respect, ceramic surface catalysts enhance catalysis by further increasing or decreasing the rate of chemical reactions. Ceramic surface catalysts are most commonly associated with and found in motor vehicles as a component of exhaust systems. This device, called a catalytic converter, contains a number of ceramic surface catalysts designed to facilitate the quick reaction of environmentally harmful engine exhausts with reagents that synthesize pollutants into more benign types of emissions. Each ceramic surface construction is covered with a different catalytic material that acts on different reagents comprising the exhaust. Alone, such reactions could not occur quickly enough to be effective. As the exhaust passes quickly over the catalyst on the ceramic surfaces, the reaction time is reduced and the result more effective.

Disadvantages of Ceramic Surface Catalysts

One of the disadvantages inherent in the design of ceramic surface catalysts is greater vulnerability to contamination due to the exposure of a maximized surface area. In this respect, the catalytic material covering the ceramic surface area may become exposed to gases or liquids with which it reacts in the absence of an additional reagent. Such occurrences may result in corrosion or dissolution of the catalytic material, thus rendering the device ineffective. To this extent, hydrogen, as the lightest of all elements, in either its stable or ionized state (a single proton) may easily bond with a ceramic surface catalyst. This action changes the composition of the catalytic material, rendering it no longer effective, particularly in the conversion of engine exhaust into more ecologically-friendly emissions.

Resource by Will

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