The effect of preparative methods on the physicochemical and catalytic properties of SiO2, TiO2 or MgO-supported rhodium catalysts

Com. SiO2 (364), TiO2 (50), and MgO (75.5 m(2)/g) were impregnated with aq. RhCl3 In the sol-gel method, aq. RhCl3 mixed with methanolic (A) Si(OMe)(4) and Ti(i-PrO)(3) and (B) 3-aminopropyltrimethoxysilane, yielded a xerogel-borne complex [Rh(3+)A(n)Cl(3)]A((5-n))5B. Catalyst precursors were examd. by TG, DTA, and MS (150-1050degreesC, 10degreesC/min), and in T-programmed reduction (TPR) and oxidation (TPO) with 50 mL/min of (5:95 v/v) H-2-Ar and O-2-He, resp., 15degreesC/min, over 50-900degreesC and 500-900degreesC, resp. On TPO, Rh 203 formed in the impregnates yielded Rh metal at 950-1050degreesC. The xerogel-borne complex decomposed in 2 steps and released Cl at 400degreesC vs. the 800degreesC required for the RhCl3 to decompose in the impregnates. Each catalyst, 0.1 g, was activated 1 h/500degreesC in H-2 and tested in the (1:1 v/v) CO2 + CH4 reaction (80 mL/min, 200-900degreesC). Activity followed the type: Rh/MgO >> Rh/SiO2 Rh/TiO2. In Rh/MgO, spinel MgRh2O4, evidenced at > 700degreesC, made Rh less sinterable. In Rh/TiO2, strong Rh-support interactions suppressed activity. The sol-gel technique yielded inadequate dispersion of the active phase and led to less active catalysts.