Computational methods feedback mechanisms

Recently there has been a growing emphasis on the use of transient methods to study the mechanism and kinetics of catalytic reactions (16, 17, 18). These transient studies gained new impetus with the introduction of computer-controlled catalytic converters for automobile emission control (19) in this large-scale catalytic process the composition of the feedstream is oscillated as a result of a feedback control scheme, and the frequency response characteristics of the catalyst appear to play an important role (20). Preliminary studies (e.g., 15) indicate that the transient response of these catalysts is dominated by the relaxation of surface events, and thus it is necessary to use fast-response, surface-sensitive techniques in order to understand the catalyst s behavior under transient conditions. 

The development of electronic instrumentation has effectively displaced mechanical devices as the prime element of coulometers. Those in use today almost universally utilize a capacitor charged by the current being measured. The capacitor is placed in the feedback loop of an operational amplifier (op amp), the output of which registers the time-integral of the current, a principle previously used in analog computation circuitry (20). One of the first to use this method for chemical coulometry was Booman in 1957 (21). The difficulty with this approach is that a capacitor of reasonable size (Booman used a 30-yF non-electrolytic capacitor, a giant of its kind) cannot accomodate sufficient charge at the potentials suitable for chemical use. This limitation has been overcome in several ways. 

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