To investigate the redox catalytic activities of the synthesized AuNPs using the olibanum gum, the researchers have selected a well-known catalytic reaction for the transformation of 4-NP to 4-AP in the presence of sodium borohydride (NaBH4). This reaction was monitored using UV–visible spectroscopy. The absorption peak of 4-NP underwent red shift from 317 nm to 400 nm immediately after addition of NaBH4, conforming change in the colour of the solution from yellow to intense yellow. This change in colour could reveal the formation of 4-nitrophenolate ions under alkaline conditions. This peak at 400 nm remained unaltered for many days in the absence of AuNPs. This indicates the inability of NaBH4 to reduce 4-NP which could be due to a very large kinetic barrier for the reduction reaction. Remarkably, on the addition of aliquot of AuNPs to nitrophenolate…show more content… The activation energy was calculated from slope (Eo/RT) by linear plot of lnk on l/T, using the Arrhenius equation k = lnA-Ea/RT, where k can be defined at given temperature (in Kelvin) as rate constant, A is a constant and R is universal gas constant. The catalytic reduction of 4-NP was studied at six different temperatures (25, 30, 35, 45, 55, 65 and 70oC) using olibanum gum capped AuNPs as catalyst. Investigation of activation energy was made as a plot of lnk and the reciprocal temperature. A plot of lnk versus l/T, shown in Figure. 10, is a linear curve for 4-NP reduction using AuNPs. It was observed that the rate of reaction to raises up for a given temperature T. Computing activation energy was performed from the graph of straight line range of lnk against l/T. The value was calculated to be 7.4 ± 1.34 k Cal/mol. The above results clearly indicated that the catalytic reaction was carried out on NPs