Herein, the dual role of trichloroethylene (TCE) in liquid-phase hydrodechlorination with Pd catalysts supported on swellable organically modified silica (SOMS), is investigated. Batch experiments with TCE-soaked Pd/SOMS showed 45% higher conversion after 4 h than dry Pd/SOMS, suggesting that TCE acts as a reactant and as a swelling-agent. Flow experiments performed with and without ethanol (external swelling-agent) exhibited similar steady-state activities, confirming that TCE itself can cause swelling. Moreover, flow experiments, regardless of whether the SOMS-supported Pd catalysts were pre-reduced or not, yielded similar steady-state conversions, suggesting that Pd(2+) is rapidly reduced by H2 dissolved in water during approach to steadystate. In-situ characterization performed under reaction conditions using time-resolved X-ray absorption spectroscopy confirmed the reduction of Pd(2+) species to Pd(0) by dissolved H2. Overall, this study shows economic viability of hydrodechlorination of TCE using Pd/SOMS by eliminating the need for an external swelling-agent as well as a catalyst pre-reduction step.