Chemistry of oxygenates on transition metal surfaces: Activation of C- H, C-C, and C-O bonds. Progress report, December 15, 1991

Technical Report · Tue Dec 31 04:00:00 EST 1991

DOI:https://doi.org/10.2172/10182066· OSTI ID:10182066

Goal is to understand the requirements for and competition between activation of C-H, C-C, and C-O bonds in the synthesis and decomposition of oxygenates on transition metal surfaces. Efforts during the past year was devoted primarily to the role of activation of {beta}-CH bonds in decarbonylation of higher oxygenates on surfaces of metals such as Rh and Pd; studies were completed of more than a dozen C{sub 1}-C{sub 3} oxygenates on Rh(111), and progress was made with reagents for which {beta}-CH scission is blocked. It is shown that alcohols and aldehydes do not react via a common pathway on on Rh(111). Ethanol and acetaldehyde are formed from CO + H{sub 2} by parallel routes on Rh catalysts which do not contain interacting supports or oxide promoters; i.e., the two compounds result from CO insertion into different metal-hydrocarbon bonds. Aldehydes decarbonylate via {alpha}-CH scission to form acyl, followed by C-C scission to release an alkyl ligand; this ligand undergoes hydrogenation and dehydrogenation steps. Alcohols form surface alkoxides, but these do not dehydrogenate further to the aldehydes, they release CO + H{sub 2} but no volatile hydrocarbon. These results indicate that {beta}-CH scissors to form a surface oxametallacycle intermediate; supporting evidence is spresented for this intermediate. Chemistry of alcohols blocked to different extends at the {beta}-position was also studied; complete blocking (CF{sub 3}CH{sub 2}OH) forces the reaction to follow the aldehyde-acyl path, while partial substitution at the {beta} position (branched alcohols) favors the oxametallacycle pathway. (DLC)

• Research Organization: Delaware Univ., Newark, DE (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-84ER13290
• OSTI ID: 10182066
• Report Number(s): DOE/ER/13290--8; ON: DE92040843
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201
ACETALDEHYDE
ALCOHOLS
ALDEHYDES
CATALYTIC EFFECTS
CHEMICAL ACTIVATION
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
ETHANOL
PHYSICAL PROPERTIES
PROGRESS REPORT
REACTION INTERMEDIATES
RHODIUM
SURFACES