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Alumina‐Supported Ni–Au: Surface Synergistic Effects in Catalytic Hydrodechlorination
Author(s) -
Keane Mark A.,
GómezQuero Santiago,
CárdenasLizana Fernando,
Shen Wenqin
Publication year - 2009
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.200900070
Subject(s) - catalysis , chemisorption , nickel , metal , activation energy , chemistry , phenol , transition metal , nuclear chemistry , materials science , inorganic chemistry , organic chemistry
Abstract Catalytic gas‐phase hydrodechlorination (HDC) of 2,4‐dichlorophenol (2,4‐DCP) has been investigated over Ni/Al 2 O 3 and Au/Al 2 O 3 prepared by impregnation, and Au–Ni/Al 2 O 3 prepared by reductive deposition of Au onto Ni. Catalyst activation by temperature‐programmed reduction is examined and the activated catalysts are characterized in terms of H 2 chemisorption, XRD and TEM‐energy dispersive X‐ray (EDX) measurements. Ni/Al 2 O 3 (<1–10 nm) and Au/Al 2 O 3 (<1–15 nm) exhibit a relatively narrow metal size distribution while Au–Ni/Al 2 O 3 bore larger particles (1–30 nm) with variable surface Ni/Au ratios. Au/Al 2 O 3 exhibits low H 2 uptake and low HDC activity to generate 2‐chlorophenol (2‐CP) as the sole product. H 2 chemisorption on Au–Ni/Al 2 O 3 was approximately five times lower than that recorded for Ni/Al 2 O 3 but both catalysts delivered equivalent initial HDC activities. Ni/Al 2 O 3 exhibits an irreversible temporal deactivation where partial dechlorination to 2‐CP is increasingly favored over full dechlorination to phenol. In contrast, thermal treatment of Au–Ni/Al 2 O 3 in H 2 after reaction elevates HDC activity with a preferential full HDC to phenol. This response is linked to a surface reconstruction resulting in a more homogeneous combination of Ni and Au. This result was also achieved by a direct treatment of Au–Ni/Al 2 O 3 with HCl. A parallel/ consecutive kinetic model is used to quantify the catalytic HDC response.