Recently, there has been a growing interest in the usage of mm-scale
composites of plasmonic nanoparticles for enhancing the rates of chemical
reactions; the effect was shown recently to be predominantly associated with
the elevated temperature caused by illumination. Here, we study the parametric
dependence of the temperature distribution in these samples, and provide
analytic expressions for simple cases. We show that since these systems are
usually designed to absorb all the incoming light, the temperature distribution
in them is weakly-dependent on the illumination spectrum, pulse duration,
particle shape, size and density. Thus, changes in these parameters yield at
most modest quantitative changes. We also show that the temperature
distribution is linearly dependent on the beam radius and the thermal
conductivity of the host. Finally, we study the sensitivity of the reaction
rate to these parameters as a function of the activation energy and interpret
various previous experimental reports. These results would simplify the
optimization of photocatalysis experiments, as well as for other energy-related
applications based on light harvesting for heat generation