As a follow-up of the paper “Engineering of silica-supported platinum catalysts with hierarchical porosity combining latex synthesis, sonochemistry and sol-gel process – I. Material preparation” (A.F. Sierra-Salazar, et at., Microporous Mesoporous Mater. 234 (2016) 207–214. http://dx.doi.org/10.1016/j.micromeso.2016.07.009), we propose waterborne Pt-based catalysts with hierarchical porosity and controlled Pt nanoparticles (NPs) distribution within the support. The materials exhibit specific surface areas and total pore volumes as high as 490 m² g⁻¹ and 0.77 cm³ g⁻¹, with ∼5 nm Pt NPs mainly located in the macropores. The Pt NPs were characterised using X-ray photoemission spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM). Considering the selectivity challenge of the catalytic hydrogenation of halonitrobenzenes to produce haloanilines, which are important raw materials for several industrial products, we evaluated these hierarchically porous catalysts for the hydrogenation of p-chloronitrobenzene (p-CNB) in batch mode to produce p-chloroaniline (p-CAN). It was possible to obtain up to 100% selectivity at 80% conversion and initial reaction rates up to 34 mol_CNB min⁻¹ mol_Pt ⁻¹. Such selectivity was higher than that exhibited by a commercial Pt/SiO₂ catalyst (up to 92%).

A novel catalyst preparation procedure is proposed in order to enhance the noble metal distribution at low loadings, while controlling the hierarchical porosity of the support material. Thus, a silica-supported platinum catalyst with hierarchical porosity was prepared using a combination of three processes performed in aqueous medium: emulsion polymerisation, sonochemistry and sol-gel synthesis. First, a polystyrene latex template of ca. 130 nm was synthesised by emulsion polymerisation and subsequently decorated with Pt nanoparticles of ca. 2.1 nm by sonochemical reduction of sodium tetrachloroplatinate. Then, the mesoporous silica support was prepared by a two-step acid-base catalysed sol-gel synthesis around the Pt-loaded latex spheres. Materials with specific surface areas and total pore volumes as high as 615 m² g⁻¹ and 0.74 cm³ g⁻¹, respectively, were obtained.