Using the MCPA, we exemplarily investigate the plasma-catalytic conversion of n-butane (C$4$H${10}$), employing ex-situ fourier transform infrared spectroscopy (FTIR) at the gas outlet to evaluate conversion efficiency and product selectivity. Systematic examination of gas composition, catalyst material, and temperature reveals that under high helium (He) dilution conditions, varying the specific energy input (SEI) by voltage from 0.05 to 0.49 eV/molecule yields a maximum conversion of 34\%. Surprisingly, the presence of the catalyst at room temperature reduces conversion to a maximum of 20\%, demonstrating an anti-synergistic effect under the applied discharge conditions. These findings highlight the need for more efficient plasma-catalyst systems to enhance conversion and improve product selectivity.