A multi-molecular beam/infrared reflection absorption spectroscopy apparatus for probing mechanisms and kinetics of heterogeneously catalyzed reaction from ultrahigh vacuum to near-ambient pressure conditions.

Abstract

A novel multi-molecular beam/infrared reflection absorption spectroscopy (IRAS) apparatus is described, which was constructed for studying mechanisms and kinetics of heterogeneously catalyzed reactions following a rigorous surface science approach in the pressure range from ultrahigh vacuum (UHV, 1 × 10-10 mbar) to near-ambient pressure (NAP, 1000 mbar) conditions. The apparatus comprises a preparation chamber equipped with standard surface science tools required for the preparation and characterization of model heterogeneous catalysts and two reaction chambers operating at different pressure ranges: in UHV and in the variable pressure range up to NAP conditions. The UHV reaction chamber contains two effusive molecular beams (flux up to 1.1 × 1015 molecules cm-2 s-1), a quadrupole mass spectrometer, a Fourier-Transform (FT) IRA spectrometer, and a molecular beam monitor for beam aligning. This combination of the methods allows us to independently dose different reactants on the surface in a highly controlled way while simultaneously monitoring the evolution of gaseous products by QMS and recording the evolution of the surface species by FT-IRAS. The second reaction chamber operating in the variable pressure range is equipped with polarization-modulation-IRAS and three gas dosers and is designed as a small reactor, which can be operated in a continuous flow mode. The sample prepared under well-controlled UHV conditions can be in situ transferred between all chambers, thus allowing for investigations of structure-reactivity relationships over model surfaces. In this contribution, we provide a detailed description of the apparatus and the test measurements of the different crucial parts of the apparatus in the variable pressure range.