Dual-path Mechanism Research Articles

An explanation of the non-linear [formula omitted] relation for the diffusion of carbon in molybdenum

Several hypotheses for the non-linear lnD versus 1 T relation for the diffusion of carbon in molybdenum are examined. Hypotheses assuming a larger mobility for carbon-vacancy pairs and for dicarbon atoms than that for single carbon atoms are ruled out experimentally. An explanation taking into account the non-linear temperature dependence of the elastic modulus is found quite satisfactory. The dual-path mechanism is not discussed because of lack of information of the carbon site in the molybdenum lattice. The elastic modulus explanation is further applied to the diffusion of nitrogen in molybdenum, which should show a similar non-linear InD versus 1 T relation.

The oxidation of formic acid on noble metal electrodes: II. A comparison of the behaviour of pure electrodes

Summary The dual path mechanism for HCOOH oxidation has been verified. The ability of Pt, Rh, Ir and Au to adsorb reaction intermediates in varying degrees has been demonstrated, together with the suggestion that the ability to chemisorb intermediates is connected with the ability to support a reaction between HCOOH and M-oxide species. It has been shown that Pd cannot adsorb COH and does not form a chemisorbed intermediate during HCOOH oxidation. This, combined with previous results, implies that COH is a major constituent of the chemisorbed intermediate formed on the other metals. The unique behaviour of Ir, having a qusi-reversible oxide region which is uniformly active towards HCOOh oxidation has been demonstrated, but not explained. The relative activities of the Pt metals and Au displayed volcano-type behaviour when correlated with the heat of formation of formate. A linear relation (with the exception of Ir) has been found between the catalytic activities of the metals towards the electro-oxidation of HCOOH and HCOOH decomposition in the gas phase.

The oxidation of formic acid on noble metal electrodes II. A comparison of the behaviour of pure electrodes

The dual path mechanism for HCOOH oxidation has been verified. The ability of Pt, Rh, Ir and Au to adsorb reaction intermediates in varying degrees has been demonstrated, together with the suggestion that the ability to chemisorb intermediates is connected with the ability to support a reaction between HCOOH and M-oxide species. It has been shown that Pd cannot adsorb COH and does not form a chemisorbed intermediate during HCOOH oxidation. This, combined with previous results, implies that COH is a major constituent of the chemisorbed intermediate formed on the other metals. The unique behaviour of Ir, having a qusi-reversible oxide region which is uniformly active towards HCOOh oxidation has been demonstrated, but not explained. The relative activities of the Pt metals and Au displayed volcano-type behaviour when correlated with the heat of formation of formate. A linear relation (with the exception of Ir) has been found between the catalytic activities of the metals towards the electro-oxidation of HCOOH and HCOOH decomposition in the gas phase.