Featured Application: Biogas and biomass producer gas cleaning.Abstract: Plasma-catalytic reforming of simulated biomass tar composed of naphthalene, toluene, and benzene was carried out in a coaxial plasma reactor supplied with nanosecond high-voltage pulses. The effect of Rh-LaCoO 3 /Al 2 O 3 and Ni/Al 2 O 3 catalysts covering high-voltage electrode on the tar conversion efficiency was evaluated. Compared to the plasma reaction without a catalyst, the combination of plasma with the catalyst significantly enhanced the conversion of all three tar components, achieving complete conversion when an Rh-based catalyst was used. Apart from gaseous and liquid samples, char samples taken at five locations inside the reactor were also analyzed for their chemical composition. Char was not formed when the Rh-based catalyst was used. Different by-products were detected for the plasma reactor without a catalyst, with the Ni-and Rh-based catalysts. A possible reaction pathway in the plasma-catalytic process for naphthalene, as the most complex compound, was proposed through the combined analysis of liquid and solid products. electron density and energy, plasma homogeneity, simple design and operation, capacity to induce reactions at relatively ambient temperature, atmospheric operational pressure, and very low level of coke production [20]. The novelty of this work lies in the combination of four problems that have so far been studied independently or in a smaller combination, i.e.,: Appl. Sci. 2020, 10, 991 A typical voltage pulse is presented in Figure 2. It does not depend on the reactor geometry, condition of the dielectric barrier, presence of catalysts, or gas composition. Its half-measured width is 9 ns, which ensures fast energization of electrons and inhibits their thermalization. This way, energy delivered to the discharge is not wasted in gas heating but consumed by electrons and further the production of radicals via electron-induced dissociation of molecules.