3.1.4. H2-TPR

Figure 3 represents the results for the reducibility of the bare silica and the calcinated samples, which were investigated by H2-TPR. Some preliminary tests of the SiO2 support showed that it did not consume any hydrogen (between 300 ◦C to 700 ◦C). Accordingly, any usage of hydrogen gas in the impregnated catalysts could be credited to the Zn metal doped on the silica support. The catalyst with 0.5% Zn loading showed the lowest maximum reduction temperature (*Tmax*) at 448 ◦C. The *Tmax* of the impregnated samples gradually raised with the elevation in Zn doping probably due to the elevation in the crystallite size of the active metal on the surface of the support. This outcome agrees with the abovementioned XRD findings. Therefore, the 3% Zn/SiO2 sample offered the uppermost maximum reduction in temperature among other catalysts (498 ◦C).

**Figure 3.** Temperature-programmed reduction profiles of the impregnated catalysts.
