Chemisorption of methyl mercaptane on titania-supported Au nanoparticles: Viability of Au surface area determination.

Well-characterized Au nanoparticles were deposited on commercial TiO(2) (P25, Degussa) and analyzed by means of STEM and thermogravimetry coupled with mass spectrometry (TG-MS). The adsorption was studied on Au/TiO(2) samples with Au loadings in the range of 1.1-9.9wt.% by injecting pulses of CH(3)SH (methyl mercaptane, MM) until no further mass increase could be observed. A prerequisite for determination of the surface area of the deposited gold nanoparticles is the proper discrimination of species adsorbing on the Au nanoparticles and the titania support. The adsorption of methyl mercaptane on the titania support strongly depended on the pretreatment temperature (30-400 degrees C), whereas the adsorption on Au nanoparticles was virtually unaffected by this parameter. A very mild thermal pretreatment was identified as a requirement for avoiding the adsorption of the MM on the titania support. CH(3)SH adsorbed on the support desorbed at lower temperatures (maximal rate of desorption was centered at ca. 150 degrees C) compared to species desorbing from Au nanoparticles (maximum at ca. 200-220 degrees C). Moreover, CH(3)SH adsorbed on Au nanoparticles desorbed in the form of dimethyl sulfide (CH(3))(2)S. Part of MM adsorbed on the gold surface was not desorbed even at high temperatures (above 500 degrees C) and stayed on the surface in the form of relatively stable C(x)H(y)S(z) fragments. This residue could be removed by oxygen pulses resulting in the formation of CO(2), SO(2), and H(2)O. The good discrimination of MM chemisorption on Au nanoparticles and on titania renders the determination of the Au surface area viable. Potential and limitations of the CH(3)SH chemisorption for the surface area determination of Au nanoparticles are discussed.