Synthesis and characterization of molybdenum carbide based catalyst for thermochemical water splitting hydrogen production

Global warming is becoming more serious due to the increasing concentration of carbon dioxide gas in the atmosphere as fossil fuels are used continuously to meet the world's energy demand. Alternatively, hydrogen can be used as an environmentally friendly and clean source of energy to reduce dependency on fossil fuels. This stucty uses the technique of producing hydrogen gas from a two-step thermochemical water splitting reaction through carburization and oxidation reaction. The M0O3 catalyst will be carburized in carbon monoxide atmosphere. A preliminary ^proach using thermodynamic calculations was performed to select Ae best activation phase for M0O3 after the carburization reaction and found that the M02C phase has the potential in hydrogen production reaction. Theoretically, the carburization reaction and splitting of water molecules is a spontaneous reaction which is AG = -86.15 kJmol'^ and -11.16 kJmol*^ at 700®C, respectively. The isothermal carburization process at 700®C yielded an average of 28.34% hydrogen production over 60 mins, 29.13% over 90 mins, and 23.84% over 120 mins. Notably, the 60 mins carburization exhibited the highest water to hydrogen conversion among these durations, widi no significant difference compared to the 90 mins carburization. However, the hydrogen production is still low compared to the theoretical 60 % selectivity. Consequently, introduction of various metals is anticipated to boost hydrogen output and reduce the temperature required for both reactions. After the addition of various metals, the hydrogen yield started to increase as follows: 1% Rh/Mo03 (31.71%) > 1% Cr/Mo03 (29.13%) > M0O3 (28.34%) > 1% CU/M0O3 (25.50%) > 1% Ni/Mo03 (22.09%), although the addition of various metal is only 1 wt.%. The addition of rhodium metal shows the highest production of hydrogen gas. The study continued by examining the effect of different Rhodium metal loadings on M0O3. The yield of hy^ogen production is 1% Rh/Mo03 (31.71%), 3% Rh/Mo03 (34.89%), 5% Rh/MoOs (24.44%) and 7% RhyMo03 (29.27%). However, only 3% Rh/MoOs catalyst showed a higher yield of hydrogen production due to the formation of the M02C active phase wfrich was most detected using XRD. Accordingly, FESEM analysis has shown that the addition of Rh metal after the carburization reaction has slightly changed the morphology of the M0O3 surface to become rougher and this is expected to allow gas absorption during the water splitting reaction. Catalyst 3% Rh/Mo03 was selected to assess its stability, as it can be regenerated for up to three cycles, with each cycle involving the introduction of 50 water v^rs dose (equivalent to 12,05 pmol per dose). The average yield of hydrogen production is around 42.34% (Cycle 1), 31.95% (Cycle 2), 24.84% (Cycle 3) and is decreasing due to the increasing carbon formation.