Temperature-programmed decomposition of the precursors of supported M/SiO2 catalysts

Merck's 364-m(2)/g SiO2, av. pore volume 2.3 cm(3)/g, was (A) impregnated with aq. Cu(NO3)(2).5H(2)O, Co(NO3)(2).6H(2)O, or Cr(NO3)(3).9H(2)O, kept 24 h/20degreesC, dehydrated, and dried in air 4 h/105degreesC to yield 3% active-phase catalysts; (B) aminated with 10 mols Si(OCH3)(4) and 1 mol 3-aminopropyltrimethoxysilane and grafted on with the metal ions to yield metalamine complexes. TG, DTG, DTA and MS revealed at least 5 thermal decomposition stages involving melting and amorphization (60-100degreesC), dehydration (100-130degreesC), and reduction (130-250degreesC (Cr), -450degreesC (Cu), -600degreesC (Co)) to NO, N2O, NO2, H2O, O-2, N-2, and HNO2 (+ trace HNO3). Crystalline CuO and Co3O4 dissociated at 1050degreesC and -650degreesC, resp.; amorphous Cr2O3 and CrO2 crystallized and yielded alpha-Cr2O3. The existing decomposition pathways were refuted and two novel were suggested, NO(3)(-)via NO or NO2 to HNO2, Thermal decomposition in the oxidizing atmosphere showed the precursors dispersed on the SiO2 surface to decompose to yield at >450degreesC pure metal oxide/SiO2 systems. The B-mode complexes decomposed in two steps: 100-250degreesC, the redox reaction involving NO3- [-NH2] and O-2 yielded mainly N-2, H2O and some NO and N2O; 250-600degreesC, the amine-hydrocarbon chains uncombined with the metal ion were oxidized to yield CO2 and H2O and some CO and N2O. 23 refs.