Characterization of sorbed intermediates and implications for the mechanism of chain growth in the conversion of methanol and ethanol to hydrocarbons over 12-tungstophosphoric acid using infrared photoacoustic spectroscopy

Journal Article · Tue Apr 01 00:00:00 EST 1986 · J. Catal.; (United States)

DOI:https://doi.org/10.1016/0021-9517(86)90313-1· OSTI ID:5206028

Highfield, J G; Moffat, J B

Photoacoustic Fourier-Transform Infrared Spectroscopy has been used to study the conversion of C/sub 1/-C/sub 4/ alcohols to hydrocarbons over 12-tungstophosphoric acid, H/sub 3/PW/sub 12/O/sub 40/. The C/sub 2/-C/sub 4/ alcohols undergo Broensted-acid-catalyzed dehydration by initially the same mechanism as that reported earlier for CH/sub 3/OH. Rapid protonation of the sorbed alcohol is followed by thermally induced C-O bond cleavage, and the resulting alkyl cation is stabilized, in varying degree, by neighboring O ions in the Keggin unit. The cycle is completed by deprotonation and olefin desorption, considered to occur preferentially for alkyl intermediates associated with the more basic O ions. For C/sub 2/H/sub 5/OH, the latter step yields C/sub 2/H/sub 4/ at 110/sup 0/-150/sup 0/C which subsequently plays an important role in chain growth. The olefin readily reacts with sorbed C/sub 2/H/sub 5//sup +/ in this temperature range to form n-C/sub 4/H/sub 9//sup +/, which quickly rearranges to i-C/sub 4/H/sub 9//sup +/. Consistent with its proposed carbenium ion character, the latter species reacts with NH/sub 3/ to form the alkylammonium cation, and further rearranges to the tertiary form above approx. = 200/sup 0/C. In CH/sub 3/OH, the onset of corresponding chain growth (and rearrangement), enhanced by the addition of C/sub 2/H/sub 4/ is observed at approx. = 175/sup 0/C. The carbene (:CH/sub 2/) mechanism of initial C-C bond (or C/sub 2/H/sub 4/) formation from sorbed CH/sub 3//sup +/ is tentatively favored over the onium ylide route. The onset of H-transfer (and carbonization) in conversion of the alcohols under static conditions is observable already at approx. = 150/sup 0/C, and becomes extensive at elevated temperature, resulting in essentially paraffins above approx. = 250/sup 0/C. Selectively suppression of the stretching vibrations of sorbed alkyl intermediates, induced by heating in vacuo, is reported.

• Research Organization: Univ. of Waterloo, Ontario (Canada)
• OSTI ID: 5206028
• Journal Information: J. Catal.; (United States), Vol. 98:2
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
ETHANOL
CATALYTIC REFORMING
METHANOL
TUNGSTOPHOSPHORIC ACID
CATALYTIC EFFECTS
ADSORPTION
ALKANES
ALKENES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
FOURIER TRANSFORMATION
GASOLINE
HYDROCARBONS
INFRARED SPECTRA
PHOTOACOUSTIC SPECTROSCOPY
REACTION INTERMEDIATES
ALCOHOLS
FUELS
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INORGANIC ACIDS
INTEGRAL TRANSFORMATIONS
KINETICS
LIQUID FUELS
ORGANIC COMPOUNDS
PETROLEUM PRODUCTS
REACTION KINETICS
REFORMER PROCESSES
SORPTION
SPECTRA
SPECTROSCOPY
TRANSFORMATIONS
010408* - Coal
Lignite
& Peat- C1 Processes- (1987-)