Surface Photochemistry of Rh(CO)2 on
Zeolite Y - Production of a Stable Coordinatively Unsaturated Rhodium
Monocarbonyl Surface Species
at Room Temperature
Xianlong Wang and Edward A. Wovchko
Department
of Chemistry
Bryn
Mawr College
101
N Merion Avenue
Bryn
Mawr, Pennsylvania 19010
Abstract
The photochemical production and chemical reactivity
of a new coordinatively unsaturated rhodium monocarbonyl species on the surface
of dealuminated zeolite Y over a temperature range of 300-420 K and a pressure
range of 10-5-20 Torr has been studied. Using high vacuum techniques and transmission infrared
spectroscopy, ultraviolet irradiation (350 ± 50 nm) of supported Rh(CO)2 surface
species led to the production of stable, but reactive, =Rh(CO) surface species,
characterized by an infrared band at 2023 cm-1. The coordinatively unsaturated =Rh(CO)
species convert to less reactive coordinatively saturated ≡Rh(CO), by
thermal treatment above 370 K. The
≡Rh(CO), species were characterized by an infrared band at 2013 cm-1. An explanation of the mode of bonding
of the rhodium monocarbonyl species to the zeolite surface was provided. Coordinatively unsaturated =Rh(CO)
species captured N2, H2, and O2 gas molecules
near room temperature to produce a variety of mixed ligand rhodium surface
complexes of the form Rh(CO)(N2), Rh(CO)(H2), Rh(CO)(H)2,
Rh(CO)(H), Rh(CO)(O), and Rh(O).
Infrared band assignments for the new species are provided. The work provides new insight into the
photochemical behavior of Rh(CO)2 species supported on high area zeolite materials, and may
improve our understanding of the role of active rhodium monocarbonyl species in
the development of heterogeneous photocatalysts.