In-situ Drift Spectroscopy in a Continuous Recycle Reactor: a Versatile Tool for Catalytic Process Research

Transmission infrared spectroscopy is a vahxable technique in catalytic science for the insitu detection and characterization of intermediates sorbed on the surface of heterogeneous catalysts (in the form of pressed-discs) under realistic conditions, i.e. high temperatures and/or high pressures. However, the drawbacks of this method are well-documented(l,2). The recent advent of commercial FTIR spectrometers, with their inherent advantages of speed and sensitivity, has led to the rapid develo~nt of alternative methods, among which Diffuse-Reflectance IR Fourier-Transform Spectroscopy (DRIFTS) permits observation of the catalyst directly in powdered or granular form(3) and appears to offer good prospects for in-situ applications, as reflected in the rapid growth of literature on this topic (see e.g. refs.49). DRIFTS circumvents many of the problems associated with the pressed-disc approach as described above but suffers from one particular weakness in its conventional form of application, viz. the& gradients across the catalyst bed@). These arise primarily from the optical constraints of the reflectance mode, which require that the sample be heated from underneath, and the fact that particulate solids are notoriously poor thermal conductors. Coupling the DRIFIS cell with a continuous recycle flow system effectively overcomes this problem by allowing the intonation of a large convention reactor in the recirculation loop. As the catalytic behaviour is now controlled essentially by the latter, the sample size in the DRIFI’S cell can be reduced (together with the associated temperature grad0920-5661/91/$03.50