The Adsortpion of CO, N2 and Li on Ru(109) and Ru(001)
The chemistry of carbon monoxide and dinitrogen on an atomically stepped Ru(109) and an atomically smooth Ru(001) single crystal surface have been thoroughly investigated using ultra high vacuum and surface science techniques. The investigations focused on the effect of the metal surface morphology on the simplest of the surface reactions: adsorption, desorption, and dissociation.
Building on the previous conclusion that CO dissociates on the step sites of Ru(109) producing mobile atomic C and O species, chemisorbed CO was bombarded with atomic hydrogen in an attempt to produce and spectroscopically observe a formyl, HCO, species by IRAS and TPD. The interaction of the two species did not produce any evidence of an HCO species, but resulted in the observation of surface crowding of the CO(a) by H(a) species.
The step sites of Ru(109) have been found to exhibit special N&sub2; adsorption characteristics compared to the terraces of the Ru(109) surface. Nitrogen desorbs from Ru(109) in three distinct desorption processes. A high temperature desorption feature has been assigned to the molecular desorption from the atomic step sites. The electron stimulated dissociation of chemisorbed nitrogen results in a high temperature recombinative desorption feature between 400 and 800 K.
A direct comparison of the vibrational behavior of nitrogen on Ru(109) and Ru(001) confirms the postulate that the step sites of single crystals exhibit special characteristics. Two vibrational bands, attributed to molecular nitrogen adsorbed on the terrace and step sites, respectively, are observed after thermal ordering of the adlayer. Nitrogen adsorbed on the terraces of the Ru(109) surface is adsorbed more strongly than on the atomically smooth Ru(001) as indicated by the lower singleton frequency on the Ru(109) surface and the lower maximum desorption temperature on the Ru(001) surface.
The interaction of adsorbed species with Li promoter atoms was investigated to determine the effect promoter atoms would have on catalytic reactions. The coadsorption of Li with CO and N&sub2; on the two Ru surfaces results in both short and long range interactions. These interactions result in a weakened molecular bond characterized by a red-shifted vibrational frequency in addition to complex formation on the surface.
Advisor:Dr. J. Karl Johnson; Dr. David Waldeck; Dr. John T. Yates, Jr; Dr. David Pratt
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Date of Publication:09/19/2007