Using density-functional theory, we performed calculations on a single-atom catalyst (SAC) comprising an iridium atom on a modified graphene oxide (Ir-1-GO) surface to investigate the conversion of CO2 and C2H6 molecules to propanoic acid. The great catalytic activity of this surface is due to the strong adsorption of C2H6 and CO2 (-0.92 and -0.56 eV adsorption energies, respectively). First, C2H6 is dehydrogenated at an oxide site of the surface to form C2H5 + OH with a barrier of height 0.63 eV; the adsorbed CO2 then reacts with ethyl to form C2H5COO or COOC2H5 with barriers of 0.95 and 1.70 eV, respectively. Less likely, the adsorbed CO2 might be hydrogenated by hydroxyl to form HCOO or COOH, with energy barriers of 1.34 and 1.49 eV, respectively. We predict that the most likely path for the conversion of the adsorbed CO2 and ethane molecules on the Ir1-graphene oxide surface would involve the formation of propanoic acid (C2H5COOH). To understand the interaction between adsorbates and surfaces, we calculated and analyzed the local densities of states (LDOS) and the electron localization function (ELF).