Three-Dimensional Imaging of Surface Chemical Processes in Catalysis Using High-Resolution Positron Emission Tomography.

Abstract

The positron emission tomography (PET) technique is a well-known method in nuclear medicine for molecular imaging of biochemical functions in the human body, but it can also be applied to molecular imaging of the chemical processes on the surfaces of heterogeneous catalysts. Dynamic studies of adsorption, desorption, and realignment of 11 C positron-emitter-labeled compounds can be performed. In the work reported herein, a small PET scanner with approximately 1.3 mm spatial resolution, originally dedicated for small-animal studies, is applied to image the location and quantitative distribution of [11 C]methanol in a catalyst bed of approximately 8 cm3 volume in three dimensions. The PET imaging technique in combination with radio-gas chromatographic analysis was also used to study different strengths of chemical bonds during catalytic processes on fresh and used Linde A-type zeolites as catalysts. The PET technique has been highly developed in the last few years with higher resolution and sensitivity and improved image reconstruction algorithms. The commercial human and small-animal PET scanners have great potential for imaging of well-functioning, poorly functioning, or partially covered catalyst surfaces in academic and industrial research for the development of catalysts. High-resolution PET scanning is a great catalysis imaging technique because of both axial and radial imaging of the catalyst bed; therefore, the distribution of radioactive compounds is analyzable in the total catalyst volume.