Adsorption of Hydrocarbons and Formation of Carbocations over Zeolites Studied by IR Spectroscopy

Abstract

Carbocation species are considered to be important intermediates in the reactions of hydrocarbons over zeolites, and the formation mechanism, as well as the reactivity, has been studied mainly by NMR and IR spectroscopy. The present state of knowledge obtained from these studies is summarized, and experimental details of IR methods for the investigation of solid catalysis are described. As an example of IR research on the catalysis of zeolites, recent results on the formation of alkenyl cation species by the reaction of cyclic alkenes with the acidic hydroxyl groups on zeolites are summarized. The formation of alkenyl cation species was observed by adsorption of cycloalkenes on silica _ alumina, HY zeolite, mordenite, H-ZSM-5 and H-beta zeolite, and characterized by IR peaks at 1490-1530 cm -1 and UV-visible peaks at 290-330 nm. Formation of alkoxyl groups in addition to alkenyl cations was observed on H-ZSM-5 with smaller pores and H-beta with weaker acidity zeolites in comparison with HY zeolite.

Surface Chemistry during Atomic Layer Deposition of Pt Studied with Vibrational Sum-Frequency Generation

“…Furthermore, it adsorbs onto the SiO 2 and Pt surfaces at temperatures that could be achieved in the ALD reactor used. 41 From this point on, the methylcyclopentene molecule will be referred to as “Me-C 5 H 7 ” to differentiate it from the MeCp ligand of the precursor. The Me-C 5 H 7 molecule was dosed onto the Pt and SiO 2 surfaces at 80 °C (the lowest possible temperature given the wall temperature).…”

The environmental applications of activated carbon/zeolite composite materials

“…(2)], and Brǿnsted acid hydroxyl groups (bridging Si-OH-Al structure) [Eqs. (3)-(4)] are featured by its great hydrogen bonding, polarized attraction forces (π-electrons), induced dipole-dipole moment and electrostatic interactions [15]. Natural zeolites [13] are abundantly extracted from a wide spectrum of volcanic rocks, ash, clay, biogenic silica and quartz [16], notably in the form of mordenite, clinoptilolite, chabaxite, erionite, phillipsite, analcime, chabazite, heulandite, natrolite, stilbite, laumontite, offretite, paulingite, barrerite and mazzite [14,17], or commercially synthesized through sol-gel deposition, centrifugation, redispersion, microwave heating, dip coating, independent tethering, calcinations, crystallization, co-condensation, carbonization (polymer/polymer blends or organic aerogel), hydrothermal treatment and templating processes (solid templating, supramolecular templating, nanocasting, or direct templating carbon nanoparticles, carbon nanotubes, mesoporous carbon, carbon aerogel and mesoscale cationic polymers) [5,8,[18][19][20][21][22].…”

Thermal and photochemical oxidation of self-assembled monolayers on alumina particles exposed to nitrogen dioxide

“…[79][80][81] It is also possible that the proximity of the hydrocarbon chain to acidic sites on the alumina surface could promote reactions leading to carbocations that react similarly to those formed in reaction (6). [82][83][84] In short, the products formed in Fig. 3a are likely a result of alumina-mediated reactions such as (6)-(11) that activate the hydrocarbon chain toward reaction with adsorbed NO x species.…”