Publikace detail

Bronsted acidity of H-MCM-22 as probed by variable-temperature infrared spectroscopy of adsorbed CO and N-2

Autoři: Delgado Montserrat R. | Bulánek Roman | Chlubna Pavla | Arean Carlos O.

Rok: 2014

Druh publikace: článek v odborném periodiku

Název zdroje: Catalysis Today

Název nakladatele: Elsevier Science BV

Místo vydání: Amsterdam

Strana od-do: 45-49

Tituly:

Jazyk	Název	Abstrakt	Klíčová slova
cze	Bronstedova kyselost H-MCM-22 byla testována pomocí infračervené spektroskopie adsorbovaných molekul CO a N2 za rozdílných teplot	Bronstedova kyselost je klíčový faktor kontrolující katalytickou aktivitu zeolitů v mnoha technologických procesech, proto je potřeba vhodné metody stanovení kyselosti v těchto materiálech.	adsorpce; vodíkové vazby; IR spektroskopie; kyselost; zeolity
eng	Bronsted acidity of H-MCM-22 as probed by variable-temperature infrared spectroscopy of adsorbed CO and N-2	Bronsted acidity is a key factor controlling catalytic performance of zeolites in many technological processes, and hence the need to find a reliable means for measuring acidity strength. The enthalpy change, Delta H-0, involved in the hydrogen bonding interaction between a weak base, such as carbon monoxide or dinitrogen, and the Bronsted acid [Si(OH)Al] hydroxyl groups should correlate with the zeolite acid strength. However, on account of simplicity, the red shift of the O-H stretching frequency, Delta nu(OH), in the hydrogen-bonded OH center dot center dot center dot CO or OH center dot center dot center dot N-2 complexes is frequently measured (instead of Delta H-0) and correlated with acid strength; and in fact it is often found that Delta H-0 and Delta nu(OH), correlate among themselves, but this might not always be the case. We report herein on a variable-temperature IR (VTIR) spectroscopic study of the interaction of CO and N-2 with the protonic zeolite H-MCM-22 (structure type MWW). From series of infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH center dot center dot center dot CO or OH center dot center dot center dot N-2 complexes was found to be -23.5(+/- 2) and -14.5(+/- 2) kJ mol(-1), respectively. Corresponding A voH values are -321 and -123 cm(-1), respectively. Comparison with corresponding Delta H-0 and Delta nu(OH) values reported in the literature for other Bronsted-acid zeolites shows strong evidence of a limited validity of the rule correlating Delta nu(OH) with Delta H-0 for both probe molecules, which gives a clear warning about the risk of using the magnitude of A voH as a measure of zeolite acidity.	Adsorption; Hydrogen bonding; IR probe molecules; IR spectroscopy; Zeolite acidity

Vyhledávání

Přihlášení pro studenty

Přihlášení pro zaměstnance

Publikace detail

Katedry

Ústavy a pracoviště

Jak nás najdete?

Služby

Často hledáte