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The water–gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen: CO + H 2 O ⇌ CO 2 + H 2. The water gas shift reaction was discovered by Italian physicist Felice Fontana in 1780. It was not until much later that the industrial value of this reaction was realized.
The first step in the WGS reaction is the high temperature shift which is carried out at temperatures between 320 °C and 450 °C. As mentioned before, the catalyst is a composition of iron-oxide, Fe 2 O 3 (90-95%), and chromium oxides Cr 2 O 3 (5-10%) which have an ideal activity and selectivity at these temperatures.
where R is the universal gas constant and T is the absolute temperature. When a single step in a reaction is perturbed in a temperature jump experiment, the reaction follows a single exponential decay function with time constant equal to a function of the forward (k a) and reverse (k b) rate constants.
The ideal temperature for a reaction under thermodynamic control is the lowest temperature at which equilibrium will be reached in a reasonable amount of time. [15] If needed, the selectivity can be increased by then slowly cooling the reaction mixture to shift the equilibrium further toward the most stable product.
In thermodynamics, a temperature–entropy (T–s) diagram is a thermodynamic diagram used to visualize changes to temperature (T ) and specific entropy (s) during a thermodynamic process or cycle as the graph of a curve. It is a useful and common tool, particularly because it helps to visualize the heat transfer during a process.
is favored by low temperatures, but its reverse is favored by high temperatures. The shift in reaction direction tendency occurs at 1100 K. [18] Reactions can also be characterized by their internal energy change, which takes into account changes in the entropy, volume and chemical potentials.
Water-gas-shift reaction. The reaction that occurs in a water-gas-shift reactor is CO + H 2 O CO 2 + H 2. This produces a syngas with a higher composition of hydrogen fuel which is more efficient for burning later in combustion. Physical separation process.
An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.