Promotion effects of an extremely low concentration of noble metals supported onto Bi2Mo3O12 on the partial oxidation of iso-butane

Supporting extremely small concentrations of noble metals on SiO 2 and Bi 2 Mo 3 O 12 affected the catalytic activity and product distribution in iso -butane partial oxidation. Supporting Pt, Pd, and Rh onto SiO 2 by 1 atom/μm 2 enhanced the catalytic activity. Selectivity values of partial oxidation products, iso -butene, CH 3 C(CH 3 )CHO, CH 3 CHO and CH 3 COCH 3 , were increased and CO x selectivity was decreased. Rh/SiO 2 gave an EPR signal due to isolated Rh 2+ ions with g ⊥ =2.07 and g ∥ =1.95, suggesting that two valent Rh ions are well dispersed on the surface and play a role in the oxidation of iso -butane. Supporting Pd, Ir, Rh, and Au onto Bi 2 Mo 3 O 12 at a concentration of (1/9)×10 −4 atom/nm 2 increased the conversion, but supporting Pt and Ru decreased it. Selectivity values of CH 2 C(CH 3 )CHO and CO x were the same for every catalyst. Catalytic activity was increased by supporting them by (1/49)×10 −4 atom/nm 2 ; especially, supporting Rh increased the activity without changing the selectivity of CH 2 C(CH 3 )CHO. Supported noble metal will interact with active oxygen ions bridging Mo and Bi on the Bi 2 Mo 3 O 12 surface. Since a certain concentration of supported noble metals, (1/49)×10 −4 nm 2 , begins to affect the catalytic activity and selectivity, this concentration may reflect the concentration of active sites in iso -butane oxidation at 350–400 °C over Bi 2 Mo 3 O 12 .