Surface science models of CoMoS hydrodesulfurisation catalysts

Characterization of supported catalysts with surface spectroscopic techniques is often limited due to restraints imposed by the support material. The use of flat conducting substrates as a model support offers a way to apply these techniques to their full potential. Such surface science models of silica and alumina supported CoMoS catalysts have been made by impregnating thin SiO2 and Al2O3 films with a solution of nitrilotriacetic acid (NTA) complexes of cobalt and molybdenum. X-ray Photoelectron Spectroscopy (XPS) spectra indicate that the order in which cabalt and molybdenum transfer to the sulfided state is reversed with respect to oxidic Co and Mo systems prepared by conventional methods, implying that NTA complexation retards the sulfidation of cobalt to temperatures where MoS2 is already formed. Catalytic tests show that the CoMoS model catalysts exhibit activities for thiophene desulfurisation and product distributions similar to those of their high surface area counterparts

Martensite Formation in Partially and Fully Austenitic Plain Carbon Steels

The progress of martensite formation in plain carbon steels Fe-0.46C, Fe-0.66C, and Fe-0.80C has been investigated by dilatometry. It is demonstrated that carbon enrichment of the remaining austenite due to intercritical annealing of Fe-0.46C and Fe-0.66C does not only depress the start temperature for martensite, but also slows the progress of the transformation with temperature compared to full austenitization. In contrast, such a change of kinetics is not observed when the remaining austenite of lean-Si steel Fe-0.80C is stabilized due to a partial transformation to bainite, which suggests that the stabilization is not of a chemical but of a mechanical nature. The growth of bainite and martensite is accompanied by a shape change at the microstructural scale, which leads to plastic deformation and thus strengthening of the surrounding austenite. Based on this stabilizing mechanism, the athermal transformation kinetics is rationalized by balancing the increase in driving force corresponding to a temperature decrease with the increase in strain energy required for the formation of martensite in the strengthened remaining austenite.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin