Hydrocarbon-induced agglomeration of Pd particles in Pd/HZSM-5

Journal Article · Thu Apr 01 00:00:00 EST 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1100· OSTI ID:6130908

Zhang, Zongchao; Lerner, B; Lei, Guandao; Sachtler, W M.H. ^[1]

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

The deactivation mechanism of Pd/HZSM-5 catalysts in the conversion of methylcyclopentane (MCP) has been studied. Results obtained with EXAFS and TEM show that agglomeration of Pd particles is the dominant cause of catalyst deactivation; no coke deposition is detected by TPO, [sup 13]C-NMR, or TEM. In a freshly reduced 0.88-wt % Pd/HZSM-5 catalyst, triatomic Pd particles are stabilized by protons bridging between Pd[sub 3] and the cage wall. During MCP reaction at 250[degrees]C the Pd[sub 3] clusters coalesce, forming much larger Pd particles of about 20 [Angstrom]. This agglomeration induces significant changes in the product distribution pattern of the isotope exchange between cyclopentane (CP) and D[sub 2]. The agglomeration is attributed to de-anchoring, i.e., the replacement of the protons in Pd[sub n]-H[sup +]-O[sub x][sup [minus]] by carbenium ions. This concept is confirmed by exposing the reduced catalyst to NH[sub 3]: proton neutralization induces formation of 50-[Angstrom] large Pd particles. Metal agglomeration is much smaller after exposure to CP instead of MCP; this evidence illustrates the crucial role of the tertiary C atom in MCP. It is concluded that the easy formation of a tertiary carbenium ion is essential for extensive deanchoring. The agglomerated Pd particles are still inside the zeolite for a low-Pd-loading catalyst, but for a catalyst with high Pd loading a significant portion of the secondary Pd particles are on the external surface. In this case the distribution of the isotope-exchange pattern of CP + D[sub 2] becomes similar to that of Pd/SiO[sub 2]. 23 refs., 14 figs., 1 tab.

• OSTI ID: 6130908
• Journal Information: Journal of Catalysis; (United States), Vol. 140:2; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
02 PETROLEUM
ALKANES
CONVERSION
PALLADIUM COMPOUNDS
CATALYTIC EFFECTS
STRUCTURAL CHEMICAL ANALYSIS
ABSORPTION SPECTROSCOPY
AGGLOMERATION
CATALYSTS
COKE
DEACTIVATION
DEPOSITION
DEUTERIUM
IONS
NUCLEAR MAGNETIC RESONANCE
PARTICLES
PROTONS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY SPECTROSCOPY
ZEOLITES
BARYONS
CHARGED PARTICLES
ELECTRON MICROSCOPY
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HYDROCARBONS
HYDROGEN ISOTOPES
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MATERIALS
MICROSCOPY
MINERALS
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RESONANCE
SILICATE MINERALS
SPECTROSCOPY
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties
020400 - Petroleum- Processing