Characterization and catalytic activity of palladium dispersed on Kratschmer–Huffman (K–H) soot

Abstract

Palladium dispersed on K-H soot, both before and after extraction with solvents, is shown to exist in a range of oxidation states and is an active catalyst for the disproportionation of cinnamyl alcohol to cinnamaldehyde and dihydrocinnamyl alcohol under conditions where a commercial Pd/C catalyst is inactive.Despite the tremendous amount of research in recent years on C60 and fullerenes in general, there have been relatively few studies on the nature of the soot produced by the Kratschmer-Huffman (K-H) technique' both before and after extraction with different solvents. There have, however, been reports describing the residual soot after extraction with solvents such as toluene and trichlorobenzene (TCB) as consisting of bucky tubes2 or giant f~llerenes.~We have recently shown4 from oxidative stability studies that K-H soot after extraction with toluene and subsequently with TCB has, rather surprisingly, a lower oxidative stability compared to fullerenes. This clearly indicated that solventextracted K-H soot still contained fullerene-like materials and was therefore different from the other forms of carbon. Consequently, since Pd/C is a well known commercial catalyst, we have in the present work dispersed palladium on K-H soot both before and after extraction with toluene and TCB, characterized the palladium/soot samples and evaluated their catalytic activity. It is shown that dispersion of Pd(N03)2 on the different soot samples, followed by reduction of the Pd(NO& with excess formaldehyde, leads to the palladium on the soot samples being present in a range of oxidation states. The dispersed palladium selectively catalyses the oxidation of one of the components of the soot. Also, these Pd/soot samples show good catalytic activity in the disproportionation of cinnamyl alcohol to cinnamaldehyde and dihydrocinnamyl alcohol. Under identical conditions, a commercial Pd/C catalyst is virtually inactive.The soot was produced by the contact-arc vaporization of graphite. 1 The condensed soot (S) was extracted repeatedly with toluene to ensure all soluble fullerenes had been extracted. This residual soot S1 was then refluxed twice with 500 ml portions of TCB and the TCB-insoluble soot coded as S2. The soot samples S1 and S2 were heated under a nitrogen atmosphere at 200 and 300 "C respectively for 4 hours to remove the last traces of any

Structure, synthesis, and catalytic properties of nanosize cerium-zirconium-based solid solutions in environmental catalysis

“…The key challenge is to find a catalyst that can achieve a high rate of soot oxidation in combination with substantial NOx reduction at sufficiently low temperature. Several kinds of catalysts such as precious metals [436][437][438][439], transition metal oxides [440], alkaline metal oxides [441], perovskite-like type oxides [442][443][444][445][446], and ceria-based oxides [285,447,448] have shown good catalytic activities for simultaneous removal of NOx and soot. Especially, CZO is one of the key components owing to its excellent OSC property and robust stability [156,214].…”

Aspects of allylic alcohol oxidation—a bimetallic heterogeneous selective oxidation catalyst

“…This minor pathway ( < 3% selectivity) was only observed at atmospheric pressure, presumably reflecting the lower surface oxygen concentration, and thus the accumulation of adsorbed hydrogen. 10 A similar side reaction has been observed over palladium/soot catalysts 16 and was likewise a function of oxygen concentration. The main role of gas-phase oxygen in aldehyde formation probably lies in the clean-off of carbonaceous residues which are believed to cause irreversible catalyst deactivation.…”

Preparation, characterisation and catalytic hydrogenation properties of palladium supported on C60

“…Similar E b behaviour has been observed in Pd dispersed on fullerene soot. 26 A series of experiments was carried out for the hydrogenation of diphenylacetylene, phenylacetylene, cyclohexene and hex-1-ene under 1 atm of in methanol, catalysed by 1 H 2 mol% of 2 at rt. Two typical reaction proüles are depicted in Fig.…”