Chemical control of the characteristics of Mo-doped carbon xerogels by surfactant-mediated synthesis

Abstract

Carbon xerogels doped with Mo were prepared by a sol–gel modified method for the resorcinol (R) – formaldehyde (F) polymerization (RF-gels). The use of surfactants (S) yields composites (RFS-gels), the S molecules are incorporated to the gel structure generating different metal anchoring sites. The interaction of molybdate ions (MoO42-) with RF and RFS-gels was analysed. The MoO42- adsorption is favoured by the attractive interactions with the RFS-gel containing a cationic surfactant, and by the presence of oxygenated chemical groups introduced by the non-ionic surfactant. The smallest Mo-loading was obtained in RFS-gels containing anionic surfactant as a consequence of repulsive interactions. The adsorbed Mo-species influence on the curing of the polymeric gels, inducing a larger shrinkage and a lower microporosity of the carbon xerogels. The dispersion and chemical nature of Mo particles depend also on the Mo-gel interactions. Stronger attractive interactions avoid sintering in some extent and favour the reduction of the molybdate with formation of a mixture of α-Mo2C and MoO3, while MoO3 particles were only found in RF-Mo or anionic RFS-Mo carbon xerogels. Only propene was obtained as product of the isopropanol decomposition showing the acid character of these catalysts. The catalytic activity is correlated to the proportion of Mo2C formed in each sample.