The hydrocarbon-selective catalytic reduction (HC-SCR) activity of an Ag/Al2O3 catalyst was investigated. The function on catalytic NOx reduction of different fuel properties using alternative reactants such as gas-to-liquid (GTL) and butanol was studied. This work proves that such improvements are due to the high reactivity, polarity and diffusivity of butanol within the catalyst enhancing NOx conversion. Furthermore, it is suggested that HC components such butanol share some of the reaction mechanisms to hydrogen as a promoter in addition to his role as a reductant leading to improve NOx reduction. Therefore, it is proposed the simultaneous dual role of butanol as a reactant and as promoter. Catalyst performance at low temperature was further improved with the addition of hydrogen (H2). However, this performance was found to degrade as temperature increases, due to H2 reactant selectivity changing, directly being oxidised. Increased NOx conversion was dependent on HC:NOx ratio, showing at low temperature a low HC:NOx ratio is required. As temperature increases, so does the required HC:NOx ratio to compensate for hydrocarbons partial and complete oxidation. These results demonstrate a method of gaining significant NOx reduction through  the combination of environmental catalysts and alternative reactants.