Activation of Novel Copper-Carbon Catalysts Using Temperature-Programmed Mass Spectometry

An entirely new method of preparing metal-carbon catalysts is reported in which the metal is present as small crystallites distributed in a three-dimensional array throughout the bulk of the carbon matrix. The metal particles are linked by a network of pores which exposes virtually all of the metal surface to the gas phase. By virtue of their structure, these new materials exhibit a remarkable resistance to sintering, even near the melting point of the metal. While many catalytically important metals can be incorporated into our materials, this paper concentrates on the structure of one of the copper-carbon systems. These are made by the reduction of a copper(II) cellulose precursor to produce a copper(0) cellulose material, followed by thermal degradation of the cellulose and activation of the resulting carbon to produce the pore network. New techniques, using a temperature-programmed gas-flow micro-reactor linked to an on-line mass spectrometer, are used to investigate the nature of the critical activation process. The resulting pore structure is studied and a mechanism is proposed to explain the catalytic effect of the copper particles on the formation of the pore network. Poisoning experiments demonstrate that access to the active sites is determined by the pore size, thus giving a measure of size selectivity. Using temperature- programmed oxidation with on-line MS it was demonstrated that the pores can be widened in a controlled manner, so reducing any diffusion-induced limitation on reaction rates. This offers the possibility of designing a catalyst with a specified balance between the conflicting requirements for size selectivity and high reaction rates.