An examination of catalyst deactivation in p-chloronitrobenzene hydrogenation over supported gold

The stability of Au/Al2O3 in the continuous gas phase (423 K) hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) has been investigated over an inlet H-2/p-CNB = 4-390, i.e. from close to stoichiometry to H2 far in excess. The catalyst (activated unused and spent) has been characterised with respect to specific surface area (SSA)/porosity, temperature programmed reduction (TPR), powder XRD, H-2 chemisorption, STEM, XPS, elemental analysis and TGA-DSC measurements. Activation of Au/Al2O3 by TPR in hydrogen generated a narrow Au size distribution (1-8 nm, mean = 3.6 nm) with evidence (from XPS) of (support -> metal) charge transfer to generate surface Au delta-. Exclusive p-CAN production was achieved under conditions of kinetic control, which were established by parameter estimation and experimental variation of contact time, catalyst particle size and p-CNB/catalyst ratio. A temporal decline in activity was observed that was more pronounced at H-2/p-CNB