Kinetic measurement technical catalysts

In flow reactors, reaction conditions more closely resemble that of the larger-scale process and the objectives are typically to measure steady-state kinetic properties for a specific gas-phase composition, temperature, flow rate, etc. In addition to being a function of its preparation and pretreatment, the steady-state kinetic parameters of a technical catalyst are a function of its reaction history and the reaction conditions during the steady-state experiment. Changes in reaction conditions... 

With the TAP approach reactions also occur at a vacuum-solid interface. However, unlike the surface science approach, the solid surface in a TAP experiment is generally a disordered technical material such as industrial catalyst particles that are generally studied in flow reactors. The objective of a TAP experiment is to measure nonsteady-state kinetic properties and track how changes in reaction conditions and sample composition alter these properties. Incrementally increasing or decreasing the amount of a single component while simultaneously making kinetic measurements charts the correspondence between a component... 

Since no synthetic chemistiy infrastructure was available at the Department (or, indeed, the Institute) before 2008, polyciystalline samples of catalysts had to be obtained from external, often industrial, partners. In order to produce model systems in house, researchers in the Department of Inorganic Chemistry developed a suite of instruments allowing the synthesis of metal oxides by physical vapor deposition of elements and by annealing procedures at ambient pressure. They chose the dehydrogenation of ethylbenzene to styrene on iron oxides as the subject of their first major study. Figure 6.6 summarizes the main results. The technical catalyst (A) is a complex convolution of phases, with the active sites located at the solid-solid interface. It was possible to synthesize well-ordered thin films (D) of the relevant ternary potassium iron oxide and to determine their chemical structure and reactivity. In parallel. Department members developed a micro-reactor device (B) allowing them to measure kinetic data (C) on such thin films. In this way, they were able to obtain experimental data needed for kinetic modeling under well-defined reaction conditions, which they could use to prove that the model reaction occurs in the same way as the reaction in the real-life system. Thin oxide... 

With the surface science approach reactions occur at a vacuum-sohd interface on an atomically ordered surface maintained at ultrahigh-vacuum (UHV) conditions. The objective is to accurately define the structure and composition of the surface, measure its chemical or kinetic properties, and establish the relationship between structure and properties. Kinetic parameters determined under UHV conditions using molecular beam scattering (MBS) and thermal desorption experiments on an atomically ordered surface can be directly related to elementary processes and can be used to construct detailed models that describe how different atomic or molecular species interact with the surface. In recent years, studies have moved beyond single crystals, and a number of groups have fabricated model catalysts with greater complexity to more closely represent the important features of technical materials (1, 2]. 

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