Ra. Koppel et al., COPPER-ZIRCONIA AND SILVER-ZIRCONIA AEROGELS - PREPARATION, STRUCTURAL-PROPERTIES AND CATALYTIC BEHAVIOR IN METHANOL SYNTHESIS FROM CARBON-DIOXIDE, Journal of catalysis (Print), 179(2), 1998, pp. 515-527
Copper- and silver-zirconia aerogels containing 10 at% IB metal were p
repared from tetra-n-butoxy zirconium(IV) and IB metal acetates using
the solution sol-gel method and ensuing high-temperature (HT) and low-
temperature (LT) supercritical drying, respectively. The influence of
preparation parameters and calcination on the structural and catalytic
properties of the aerogels for the synthesis of methanol from carbon
dioxide and hydrogen was investigated. After calcination in air at 573
K, the catalysts had BET surface areas in the range of 100-143 m(2) .
g(-1) (Cu/ZrO2) and 77-125 m(2) . g(-1) (Ag/ZrO2), respectively. Due
to the reductive alcoholic atmosphere during high-temperature supercri
tical drying, metallic copper and silver existed in all raw HT-aerogel
s. The mean size of the copper crystallites was 30 nm. The silver crys
tallite size for the HT-aerogel prepared with nitric acid was 10 nm, w
hereas for samples prepared with acetic acid it was 5-7 nm. Calcinatio
n in air at 573 K led to the formation of highly dispersed amorphous c
opper oxide and silver. Comparing the catalytic behavior of the calcin
ed copper-zirconia aerogels with corresponding xerogels prepared by co
precipitation revealed highest activity for the LT-aerogel, whereas th
e HT-aerogels were least active. In contrast, similar catalytic behavi
or was observed for the differently dried silver-zirconia samples. Gen
erally, CO2-conversion of the copper-zirconia aerogels was markedly hi
gher than that of the corresponding silver-zirconia aerogels, whereas
methanol selectivity was similar. (C) 1998 Academic Press.