Elucidating the promotional effects of niobia on SnO₂for CO oxidation: developing an XRD extrapolation method to measure the lattice capacity of solid solutions

Abstract

Using an XRD extrapolation method, the SnO2 lattice capacity for Nb2O5 is quantified. A Sn–Nb solid solution without excess Nb2O5 is promising for CO oxidation.

The Influence of RuO2Distribution and Dispersion on the Reactivity of RuO2−SnO2Composite Oxide Catalysts Probed by CO Oxidation

“…However, both SnRuO-CP samples possess evidently higher surface areas of 23 m 2 g À 1 , further confirming that the formation of solid solution structure can impede the crystallization of the catalysts, which is in accordance to the XRD crystallite size results. [27,28,30] In summary, both XRD, Raman and N 2 -BET results have provided strong evidence to demonstrate that in SnRuO-IMP and SnRuO-DP samples, RuO 2 disperses mainly on the SnO 2 support surface as micro crystallites but with different sizes. With impregnation method, catalysts having smaller RuO 2 crystallite sizes can be obtained than with deposition-precipitation method, which is believed to be favorable to the activity.…”

“…However, for SnRuO-CP samples, which were prepared with co-precipitation method, there is a high possibility that Ru species enters into the lattice matrix of tetragonal SnO 2 first as Ru 4 + cations to form a non-continuous solid solution structure with a certain capacity. [27,28] Until the Ru 4 + amount reaches the lattice capacity, RuO 2 micro crystallites will then be formed on the Sn-RuÀ O solid solution surface and become detectable by XRD. [27,28] As discussed in our previous work, if two metal cations have close radii and similar oxidation states, a solid solution structure inclines to be formed by dissolving the solute cations into the lattice of a solvent metal oxide with a certain lattice capacity.…”

“…[27,28] Until the Ru 4 + amount reaches the lattice capacity, RuO 2 micro crystallites will then be formed on the Sn-RuÀ O solid solution surface and become detectable by XRD. [27,28] As discussed in our previous work, if two metal cations have close radii and similar oxidation states, a solid solution structure inclines to be formed by dissolving the solute cations into the lattice of a solvent metal oxide with a certain lattice capacity. In this work, SnO 2 , as the solvent oxide, has a rutile crystalline structure, in which Sn 4 + has a coordination number (CN) of 6 and a radius of 0.69 Å.…”

“…Indeed, this indicates further that the Ru 4 + cations can dissolve into SnO 2 lattice matrix to form a solid solution structure, hence hampering the crystallization of the SnO 2 phase during the calcination process. [27,28,30] All the 2 %SnRuO samples have been analyzed by Raman, with the spectra displayed in Figure 4. Pure SnO 2 shows four Raman bands at about 475, 633, 690 and 774 cm À 1 , which can be assigned in sequence to E g , A 1g , A 2u and B 2g vibration of rutile SnO 2 .…”

“…It has been previously found that by forming solid solution structures, lattice distortion and defects generally occur, thus facilitating the formation of more abundant surface mobile oxygen species. [27,28,41] Therefore, it is not difficult to understand that 2 % SnRuO-CP possesses the most abundant loosely bounded surface oxygen species. Based on the reaction and characterization results discussed above, it is believed that the amount of surface dispersed RuO 2 , which can effectively adsorb and activate CO and O 2 molecules, is the crucial factor to determine the reactivity of the catalysts.…”