Armando Borgna

Synergism of Co and Mo in the catalytic production of single-wall carbon nanotubes by decomposition of CO

The catalyst composition and operating conditions for the synthesis of single-wall carbon nanotubes (SWNT) from CO decomposition have been systematically varied in order to maximize the selectivity towards SWNT. A simple quantification method based on the standard Temperature Programmed Oxidation (TPO) technique has allowed us to determine the distribution of the different forms of carbonaceous deposits present on the catalysts after the CO decomposition reaction. A synergistic effect between Co and Mo has been observed. When both metals are simultaneously present, particularly when Mo is in excess, the catalyst is very effective. However, when they are separated they are either inactive (Mo alone) or unselective (Co alone). To understand this synergistic effect, X-ray absorption spectroscopy (EXAFS and XANES) has been used to characterize the state of Co and Mo on the catalysts before and after the production of SWNT.

A Scalable Process for Production of Single-walled Carbon Nanotubes (SWNTs) by Catalytic Disproportionation of CO on a Solid Catalyst

Existing single-walled carbon nanotube synthesis methods are not easily scalable, operate under severe conditions, and involve high capital and operating costs. The current cost of SWNT is exceedingly high. A catalytic method of synthesis has been developed that has shown potential advantages over the existing methods. This method is based on a catalyst formulation that inhibits the formation of undesired forms of carbon; it can be scaled-up and may result in lower production costs.

Characterization of the morphology of Pt clusters incorporated in a KL zeolite by vapor phase and incipient wetness impregnation. Influence of Pt particle morphology on aromatization activity and deactivation

Abstract Two series of Pt/KL catalysts with varying metal loading were synthesized by the methods of incipient wetness impregnation (IWI) and vapor phase impregnation (VPI) to compare the effects of the different morphologies that result when the metal loading and, in particular, the preparation method are varied. Catalysts were characterized by a variety of techniques. TEM and DRIFTS studies indicated that on the low-loading samples the majority of particles were located inside the channels of the L-zeolite. In agreement with recent studies, the DRIFTS results evidenced the formation of Pt carbonyls, which further support the presence of very small particles. EXAFS and TEM showed that the VPI catalysts resulted in smaller particles than the catalysts prepared by the IWI method. In addition, EXAFS demonstrated for this series a higher degree of interaction with the L-zeolite framework oxygen atoms. Pulse testing of the methylcyclopentane ring opening showed that the very small clusters produced by the VPI preparation did not result in collimation of the MCP molecule, implying that the reactants and products can easily diffuse over the Pt cluster. This is in contrast with the particles produced by the IWI method, which clearly displayed a collimation effect. The characteristic morphology produced by the VPI method was found to improve the performance of the catalyst under clean and sulfur-poisoned conditions, enhancing the catalyst’s resistance to the formation of coke and decreasing the particle agglomeration rate.

Regeneration and oxidation-reduction cycles of vapor phase and incipient wetness impregnation Pt/KL catalysts

The regeneration of three different Pt/KL catalysts has been studied after the n-hexane aromatization reaction in the presence of sulfur. It has been found that regeneration in air of poisoned catalysts does not result in recovery of the aromatization activity. After this regeneration, growth of Pt particles outside the channels of the zeolite is observed. By contrast, regeneration with addition of a halo-alcohol results in Pt redispersion and significant recovery of aromatization activity. The preparation method employed and the presence of Tm as a promoter plays an important role in the efficiency of the regeneration procedure.