Ortho-Parahydrogen Conversion

Gold forms a continuous series of solid solutions with palladium, and there is no evidence for the existence of a miscibility gap. Also, the catalytic properties of the component metals are very different, and for these reasons the Pd-Au alloys have been popular in studies of the electronic factor in catalysis. The well-known paper by Couper and Eley (127) remains the most clearly defined example of a correlation between catalytic activity and the filling of d-band vacancies. The apparent activation energy for the ortho-parahydrogen conversion over Pd-Au wires wras constant on Pd and the Pd-rich alloys, but increased abruptly at 60% Au, at which composition d-band vacancies were considered to be just filled. Subsequently, Eley, with various collaborators, has studied a number of other reactions over the same alloy wires, e.g., formic acid decomposition 128), CO oxidation 129), and N20 decomposition ISO). These results, and the extent to which they support the d-band theory, have been reviewed by Eley (1). We shall confine our attention here to the chemisorption of oxygen and the decomposition of formic acid, winch have been studied on Pd-Au alloy films. 

EPR has been observed and studied in porous carbons by numerous authors 178-182). The carbons studied have been prepared by pyrolysis of organic material such as dextrose 180), coal 181), and natural gas or oils 181,182). Porous carbons are of considerable technological importance and show catalytic activity for the ortho-parahydrogen conversion, the hydrogen-deuterium reaction, and many reactions of inorganic complex ions 156). Relationships between the characteristics of the EPR absorption and the catalytic activity of porous carbons for the o-p Hj and Hj-D reactions have been demonstrated by Turkevich and Laroche 183). 

Few of the many known ferromagnetic solids are suitable as catalysts for the nondissociative ortho-parahydrogen conversion. This is especially true if measurements are needed in the neighborhood of the magnetic phase transition, Tc. The reasons for this are threefold the solid may decompose at the temperature necessary to free the surface from contaminants, the Curie point may be so low that the experimental difficulties are formidable, and many such solids show strong dissociative conversion activity near Tc. Of the three solids named above none is very satisfactory. 

EFFECT OF ADSORBED NITROGEN ON CATALYTIC ACTIVITY OF ORTHO-PARAHYDROGEN CONVERSION CATALYSTS... 

Fig. 2. Ortho-parahydrogen conversion as a function of flow rate—Rutr 3.

Table I. Run 3— Variation in Ortho-Parahydrogen Conversion with Flow Rate...

Fig. 4. Effect of nitrogen adsorption upon ortho-parahydrogen conversion.

Fig, 5. Relationship between ortho-parahydrogen conversion activity and nitrogen adsorption. 

The Gas Phase Heterogeneous Catalysis of the Ortho-Parahydrogen Conversion at Low Temperatures Under Pressure (1) 280... 

A Kinetics Study of Ortho- Parahydrogen Conversion (5) 511 OXYGEN... 

Ortho-Parahydrogen Conversion and Hydrogen-Deuterium Equilibration over Carbon Surfaces, Y. Ishikawa, L. G. Austin, D. E. Brown, and P. L. 

Ortho-parahydrogen conversion in the presence of various catalysts has occupied the attention of investigators from the early thirties to the present time, " It has been fairly well established that heterogeneous catalysis is due to interaction between adsorbed molecules and the inhomogeneous magnetic field caused by more or less isolated magnetic centers on the surface of the catalyst. Most of the... 

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