Neopentane conversion catalyzed by Pd in L zeolite: Effects of protons, ions, and zeolite structure

Journal Article · Tue Jun 01 04:00:00 EDT 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1144· OSTI ID:6153670

Karpinski, Z; Gandhi, S N; Sachtler, W M.H. ^[1]

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1. Northwestern Univ., Evanston, IL (United States)

The conversion of 2,2-dimethylpropane (neopentane) has been studied over zeolite-L-supported Pd catalysts; the results are compared with data for Pd on zeolite Y. Variation of the charge compensating ion (Li[sup +], K[sup +], or Ca[sup 2+]) in L has only a moderate effect on the catalytic parameters, due either to variations in the heat of physisorption or to [open quotes]electronic[close quotes] effects on Pd. The reduction temperature, T[sub r], of Pd/L samples that have previously been calcined at 250[degrees]C, strongly affects the catalytic performance: after T[sub r] 250[degrees]C, sufficient NH[sub 3] ligands of the ion exchanges Pd(NH[sub 3])[sub 4][sup 2+] ions survive to neutralize the protons that are formed during reduction; catalytic activity then increased during reaction while NH[sub 4][sup +] ions decompose and Pd-proton adducts of high catalytic activity are formed. At T[sub r] = 400[degrees]C, the NH[sub 3] ligands are destroyed and this catalyst is stable and very active. Activity, selectivity, and kinetic parameters depend on the structure of the support; apparent activation energies, E[sub a], are in the range of 45-55 kcal/mol for Pd/Y, but 75-90 kcal/mol for Pd/L. A linear relation between E[sub a], are in the range of 45-55 kcal/mol for Pd/Y, but 75-90 kcal/mol for Pd/L. A linear relation between E[sub a] and log of the preexponential factor is obtained. While classical pore-diffusion operates in Y, single-file diffusion appears more likely in L; i.e., channels tend to be plugged with physisorbed molecules at low temperature. The difficulty of primary reaction products to escape from the pores correlated with a higher fraction of secondary products observed for Pd/L vis-a-vis Pd/SiO[sub 2]. It is conceivable that different diffusion types also contribute to the different E[sub a] values for zeolites with three-dimensional or unidimensional channel systems. 20 refs., 5 figs., 4 tabs.

• OSTI ID: 6153670
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 141:2; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400 -- Petroleum-- Processing
2-2-DIMETHYLPROPANE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
ADSORPTION HEAT
ALKANES
BARYONS
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHARGED PARTICLES
CHEMICAL REACTIONS
CONVERSION
ELEMENTARY PARTICLES
ELEMENTS
ENERGY
ENTHALPY
FERMIONS
HADRONS
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IONS
MATERIALS
METALS
MINERALS
NUCLEONS
ORGANIC COMPOUNDS
PALLADIUM
PHYSICAL PROPERTIES
PLATINUM METALS
PROTONS
REDUCTION
SILICATE MINERALS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
ZEOLITES