CO2 was only detected in less than 0.6 vol% (Table 4), whereas higher quantities of CO were detected in the pyrolysis-gases (up to 13 vol%), suggesting that Z-YVAD-FMK a significant portion of the CO2 might be converted to form H2 and CO by heterogeneous reactions, such as dehydrogenation (R8) and dry-reforming (R9) reactions that have been reported to be promoted under microwave pyrolysis environment  and . Both the concentrations of CO2 and aliphatic hydrocarbons (particularly CH4) were found to decrease when using increased amounts of the metallic-char (Table 4). This supports the proposed increased occurrence of these heterogeneous reactions that had resulted in higher productions of H2 and CO in the pyrolysis-gases.
The results revealed that the increase in the amount of metallic-char added to the waste oil led to a reduction in the subsequent yield of additional char product (Fig. 9), suggesting that a portion of the char product (generated by the decomposition of hydrocarbons, (R1) and (R4)) was converted to H2 and CO by gasification Reaction (R7). These gasification reactions were likely to occur due to the ability of the metallic-char to absorb the microwave energy and heat up, transforming into hot spots and in turn promoting the occurrence of these reactions. These gasification reactions are a few of the heterogeneous reactions that were reported to be highly promoted in microwave pyrolysis systems  and , and they were found to occur in microwave pyrolysis systems even at low reaction temperatures of 400 and 500 °C , thus the yield of char product was reduced in favor of H2 and CO formation.