Laser Effects On Catalytic Reactions: Decomposition Of HCOOH On Pt

The effect of CO2 laser radiation on the Pt-catalyzed decomposition of HCOOH has been investigated in a static reactor and in a low-pressure matrix isolation system. HCOOH is known to decompose on Pt by two reaction paths, one leading to CO2 + H2, and the other to CO + H2O. It was found in this study that the laser caused either a decrease in the rate of formation of both CO and CO2, or selectively decreased the yield of CO, depending upon the condition of the Pt surface. In the case of a clean Pt surface, a laser line that is strongly absorbed by HCOOH caused a decrease in the rate of formation of both CO and CO2. A nonabsorbed line had no effect. In the case of a Pt surface that had been partially poisoned by reaction products, the strongly absorbed line caused a selective decrease in CO formation, thus enhancing the CO2/CO product ratio by as much as 50%. The activation energy measured for HCOOH decomposition in the matrix isolation experiments is 3.5 ± 0.2 kcal/mole using a clean Pt surface under the low pressure conditions. Additionally, the 0=C-0-H radical has been identified by the use of deuterium substitution. The present results have demonstrated the possibility of combining the unique properties of both catalysts and lasers to drive chemical reactions in selected synthetic routes and also the utility of the matrix isolation technique for heterogeneous catalytic studies.