  An environmental cell high resolution electron microscope (EHREM) has been
developed for in situ studies of dynamic chemical reactions on the atomic
scale. It allows access to metastable intermediate phases of catalysts and to
sequences of reversible microstructural and chemical development associated
with the activation, deactivation and poisoning of a catalyst. Materials
transported through air can be restored or recreated and samples damaged, e.g.
by dehydration, by the usual vacuum environment in a conventional electron
microscope can be preserved. A Philips C M30 HRTEM and STEM system has been
extensively modified in our laboratory to add facilities for in situ gas-solid
reaction studies in controlled atmospheres of gas or vapor at pressures of 0 to
50 mbar, instead of the regular TEM high vacuum environment. The integrated new
environmental cell capability is combined with the original 0.23 nm TEM
resolution, STEM imaging (bright field and annular dark field) and chemical and
crystallographic microanalyses. Regular sample holders are used and include hot
stages to higher than 1000 C. Examples of applications include direct studies
of dynamic reactions with supported metal particle catalysts, the generation of
defects and structural changes in practical complex oxide catalyst systems
under operating conditions and carbon microstructures.
