Oscillatory Behavior and Anomalous Heat Evolution in Recombination of H₂ and O₂ on Pd-based Catalysts

Abstract

Gas flow-through microcalorimetry has been applied to study the Pd/Al2O3 type catalysts in the exothermic hydrogen recombination process: H2 + O2 → H2O, in view of the potential application in the passive autocatalytic recombination (PAR) technology. The flow mode experiments revealed thermokinetic oscillations, i.e., the oscillatory rate of heat evolution accompanying the process and the corresponding oscillations in the differential heat of process, in sync with oscillatory conversion of hydrogen. Mathematical evidence has been found for the deterministic character of the aperiodic oscillations. In the outburst of quasiperiodic oscillations of large amplitude, the instances of differential heats as high as 700 kJ/mol H2 have been detected, exceeding the heat of the gaseous water formation from elements (242 kJ/mol H2) by a factor of nearly 3. Another occurrence of anomalously high thermal effects has been measured in calorimetric oxygen titration using 0.09 μmol pulses of O2 injected onto hydrogen- or deuterium-saturated catalysts, including 2%Pd/Al2O3, 5%Pd/Al2O3 and 2%PdAu/Al2O3. Repeatedly, the saturation/oxidation cycles showed the heat evolutions in certain individual O2 pulses as high as 1100 kJ/mol O2, i.e., 550 kJ/mol H2, again 2 times as much as the heat of water formation. It has been pointed out that it seems prudent for the PAR technologists to assume a much larger rate of heat evolution than those calculated on the basis of a standard thermodynamic value of the heat of water formation, in order to account for the possibility of large thermokinetic oscillation occasionally appearing in the recombination process of hydrogen. A possible relation of the anomalous heat evolution to an inadvertent occurrence of low energy nuclear reaction (LENR) phenomena is also briefly considered.

Humidity induced deactivation of Al2O3 and SiO2 supported Pd, Pt, Pd-Pt catalysts in H2+O2 recombination reaction: The catalytic, microcalorimetric and DFT studies

“…In our laboratory, we have also observed the thermokinetic oscillations, i.e., oscillatory rate of heat evolution, in the H 2 oxidation on certain Pd/Al 2 O 3 catalysts. We discuss this phenomenon in a more systematic way in another article [47], in which we are reporting the thermokinetic oscillations in the hydrogen oxidation, including periods of mathematical chaos, as well as the accompanying thermal effects occasionally exceeding the heat of water formation by a factor of ca. three.…”

Surface-Structure Libraries: Multifrequential Oscillations in Catalytic Hydrogen Oxidation on Rhodium

“…In case of H 2 oxidation, self-sustained oscillations were observed on polycrystalline Pt and Pd wires, , polycrystalline Pt layers, or supported Pd and Rh catalysts , under atmospheric pressure conditions. Under high vacuum conditions, oscillations in H 2 oxidation have been observed only on well-ordered bimetallic Rh/Ni surface alloys and on sharp Rh nanotips under high electric field conditions (>10 V/nm) .…”

Visualizing catalyst heterogeneity by a multifrequential oscillating reaction

“…Despite the increasing importance of hydrogen-based energy generation in fuel cells 16 , much less attention has been given to (oscillating) catalytic H 2 oxidation. There are only few reports on oscillating H 2 oxidation on polycrystalline Pt and Pd wires 17 , 18 , polycrystalline Pt layers 19 , or supported Pd and Rh catalysts 20 , 21 under atmospheric pressure conditions. Under high vacuum conditions, enabling microscopic studies of H 2 oxidation, oscillations have been observed only on well-ordered bimetallic Rh/Ni surface alloys 22 and on sharp Rh nanotips under high electric fields (>10 V/nm; with the applied field causing the oscillations by stimulating the periodic formation of Rh surface oxide 23 ).…”