TiO2:MoO3 nanocomposites with MoO3 content in the range of 0.1-10 mol.% were synthesized using sol-gel technology. The role of the structural peculiarities of TiO2:MoO3 composite in hydrogen adsorption and catalytic oxidation was discussed. Possibility of the selective oxidation of hydrogen in the presence of methane in the atmosphere was demonstrated.
Introduction of molybdenum trioxide to gas sensing materials based on titanium dioxide results in a considerable increase of the output signal in the hydrogen-air environment. It is established that the value of the output signal reaches the maximum at the 1 mol. % MoO 3 content in the composite material. Improved gas sensing characteristics of TiO 2 :MoO 3 composite correlate with the structural and phase peculiarities of this system – the inhibition of TiO 2 crystallization in the TiO 2 :MoO 3 system, the shift of anatase-rutile phase transition to the higher temperature area in comparison with the temperature of this transition in unloaded TiO 2 , and with the presence of different types of tetrahonal distortions in MoO 6 octahedrons, which ensures the MoO 3 lattice high activity in the processes of hydrogen catalytic oxidation, and also with the crystallization of highly dispersed molybdenum oxide with a particle size of 10 nm.
The nature and character of changes during thermal annealing of paramagnetic centers in TiO 2 –MoO 3 gas-sensing materials with 1–10 mol% MoO 3 content were studied. The results suggested that certain processes occurred in the sensor during thermocatalytic detection of combustible gases. It was found that an increase of the sensor output signal in the temperature range 200–350°C was due to active participation of MoO 3 lattice oxygen in catalytic hydrogen oxidation processes.
Thermostimulated molecular alteration in TiO2:MoO3 composite materials, obtained by sol–gel method, were investigated by IR-spectroscopy, Raman spectroscopy, and ESR spectroscopy. Change of the coordination environment of molybdenum atom from tetrahedral to octahedral in 200–450°C temperature range was revealed. Two groups of molybdenum paramagnetic centers with different saturation character, responsible for oxygen redistribution in the material were detected.
We have studied the distinctive features of the reaction between titania and molybdenum trioxide in the sol-gel synthesis of TiO 2 /MoO 3 composite materials (1–10 mol % MoO 3 ). The results demonstrate that interactions between phases, which depend on MoO 3 concentration in the composites and are stronger at higher heat-treatment temperatures, lead to suppression of titania crystallization, inhibit the anatase-to-rutile phase transition, and influence the morphology and structural perfection of the oxide phase.
The influence of aluminium and gallium oxides addition on gas-sensitive properties of assorted oxide structures on the base of In2O3 was investigated. It was established that addition of gallium to the structure of indium oxide makes it possible to raise the output signal of sensors and their sensitivity. According to the data obtained from the physicochemical investigations improvement of the gas-sensitive characteristics of In2O3 correlate with structural chemical changes which take place in indium oxide at doping of gallium. In the aspect of the gas-sensing characteristics optimal Ga : In ratio in Ga2O3–In2O3 system is connected with appearance of a heterostructure which consists of rhombohedral and cubic indium oxide, β-Ga2O3 and (Ga,In)2O3 phases.
