Alumina Supported Au-Ni: Surface Synergism in the Gas Phase Hydrogenation of Nitro-Compounds

The catalytic gas phase hydrogenation of 1,3-dinitrobenzene over Au/Al2O3 delivered exclusive reduction of a single -NO2 substituent to generate 1,3-nitroaniline (E-a = 131 kJ mol(-1)), reaction over Ni/Al2O3 resulted in full hydrogenation to 1,3-phenylenediamine (E-a = 38 kJ mo1(-1)), whereas both products were isolated over Au-Ni/Al2O3. In the hydrogenation of 1,3,5-trinitrobenzene, Au/Al2O3 promoted preferential partial hydrogenation (3,5-dinitroaniline), Ni/Al2O3 generated 1,3,5-triaminobenzene as the predominant product, while Au-Ni/Al2O3 exhibited an intermediate catalytic response. The catalysts have been characterized in terms of temperature programmed reduction (TPR), H-2 chemisorption, powder XRD, high-resolution TEM, XPS, and XANES/EXAFS measurements. Post-TPR, there was evidence of a metal particle redispersion resulting from the introduction of Au to Ni/Al2O3 where HRTEM-EDX mapping has established close proximity of Au and Ni on Au-Ni/Al2O3 with electron transfer from Ni to Au (from XPS analysis). Hydrogen chemisorption on Au-Ni/Al2O3 was 3 times lower than that recorded for Ni/Al2O3, suggesting Au-Ni interaction that inhibits H-2 uptake. Simulation of the XANES/EXAFS response provided a better fit when incorporating Au-Ni interaction. The results demonstrate control of selectivity in poly nitroarene hydrogenation through the use of mono- (Au and Ni) and bi- (Au-Ni) metallic catalysts, where catalytic response is governed by surface composition.