In Situ IR Study of the Nature and Mobility of Sorbed Species on H-FER during But-1-ene Isomerization

Abstract

The sorption and reaction of but-1-ene over a ferrierite sample was studied by in situ IR spectroscopy to relate the selectivity to isobutene and the sorbed species. The spectra highlighted the presence of various unsaturated species including polyenes, which were readily formed upon contacting H-FER with but-1-ene while a poor selectivity to isobutene was observed. Aromatic compounds were concluded to be subsequently formed via dehydrogenation/cyclization of the polyenic deposits while the isobutene selectivity increased via suppression of by-products. These data support earlier assumptions that the initial high yield of by-products was produced by the reaction of butenes with reactive deposits, which were gradually converted into more inert aromatic deposits. Upon purging the catalyst with an inert, branched C 8 hydrocarbons and aromatic molecules such as xylenes desorbed. The rates of desorption showed an initially linear variation with the square root of time and were fitted to a monodimensional Fickian model. Because the slowly diffusing species were rather abundant during the course of the reaction, it is proposed that the skeletal isomerization was effectively limited to the acid sites close the pore mouth of H-FER crystallites. c 2002 Elsevier Science (USA)

Effects of temperature and rich-phase composition on the performance of a commercial NOx-Storage-Reduction material

“…It is therefore unlikely that this band related to a surface carbonate 7 species. Alkenes can readily decompose to cationic allylic species on acidic sites, which lead 8 to a strong band at around 1575 cm -1 [43,44]. The (oxi)dehydrogenation and aromatisation of 9 propene catalysed by the metals present could be envisaged and would lead to bands in the 10 same region.…”

Large Ferrierite Crystals as Models for Catalyst Deactivation during Skeletal Isomerisation of Oleic Acid: Evidence for Pore Mouth Catalysis

“…[13] Pore mouthc atalysish as also been postulated as an explanation for the increasei ns electivity shown by protonated ferrierite (H-FER)a tl ongert ime-on-stream (TOS)i nt he butene to isobutene alkyl isomerisation. [14][15][16][17] Here, the concept of pore mouthc atalysisi sl imited to the location of reaction at the extremities of the pores, since steric factors in the approacht o the channel are less important with such small molecules. In this medium-porezeolite, the 10-membered ring (10-MR) channels (4.2 5.4 ) are perpendicularly crossed with the 8-MR channels (3.4 4.7 ).…”

“…The improvemento ft he isobutene se-lectivity,r esulting from the decrease in cracking reactions, correlatesw ith build-up of hydrocarbond eposits in the pore system. [14,15] The filling of the volume of the H-FER zeolite crystal by slowly diffusing carbonaceouss pecies, [16] the beneficial influenceo ft he pore mouth ellipticity as well as the improved isomerisation activity observed with smaller crystallites [17] have all been listed as experimental evidence for the concept of pore mouth catalysis.…”

Detailed Process of Adsorption of Alkanes and Alkenes on Zeolites

“…A range of experimental techniques have been used to measure the diffusivity in zeolites, including the frequency response, 10 pulsed field gradient (PFG) nuclear magnetic resonance (NMR), 11 zero-length column (ZLC), 12 quasi-elastic neutron scattering (QENS), [13][14][15] positron emission profiling (PEP), 16 one-dimensional-exchange 13 C NMR methods, 17 and Fourier transform infrared spectroscopy (FTIR). 18,19 Molecular simulations have also become a powerful tool for studying adsorption on zeolites, and a number of different methods have been reported. [20][21][22][23][24] The shape selectivity (pore size) and density and type of Brønsted acid sites (BASs) are considered to affect the diffusion process.…”