ISSN:
1572-879X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Mono- and multimetallic Ni/NaY samples have been studied by static and dynamic techniques. The reducibility of Ni is dramatically enhanced by Pt clusters in supercages and by Mn ions blocking small zeolite cages. No H2 is trapped by NaY, but for Ni/NaY, NiPt/NaY, or NiPtMn/NaY more H2 is released in temperature programmed “desorption” (TPD) than can be adsorbed at 25 °C. Two phenomena are responsible for the apparent discrepancy between ad- and desorption: (1) Ni inside small cages can ad- and desorb hydrogen only when cage windows are widened by thermal vibration to permit passage of H2. (2) Above 500 °C the original reduction process Ni2+ + H2 = Ni0 + 2H+ is reversed, i.e. Ni atoms are oxidized by hydroxyl groups. This is confirmed by the H2 consumption in subsequent reduction. The high-temperature TPD feature can be used to estimate the amount of reduced Ni that is located in small cages.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00772772
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