Controllable preparation of metal oxide nanoparticles and Ni/CeO2 catalysts by microdroplets extraction and separation technology in mini-channel

The microreactor coupled mini-channel microdroplets extraction and separation technology (MES) was developed by adding polyvinyl alcohol (PVA) into microdroplets, realizing the controllable synthesis of a series of mono-component and multi-component metal oxide nano particles (MONPs). A double-layer surfactant structure composed of Span20 (oil phase surfactant) and PVA (water phase surfactant) was designed as a barrier to intercept and collect the precipitated salt at the microdroplet interface, the addition of PVA reduces the loss of salt components during the extraction process from 41.7 wt% to 1.1 wt%. The size control of mono-component MONPs (CuO, Co 3 O 4 , and NiO) was achieved using MES method. Furthermore, in the application direction of preparing multi-component MONPs, the advantages of MES in preparing multi-component catalysts (Ni/CeO 2 ) were verified. TEM, XRD, H 2 -TPR, CO 2 -TPD, XPS, BET et al. characterizations have shown that Ni entered the lattice of CeO 2 during precipitation to form a Ni-O-Ce solid solution and was therefore highly dispersed in CeO 2 . Ni/CeO 2 -MES showed high CO 2 conversion and CO selectivity in reverse water gas shift (RWGS) testing compared to Ni/CeO 2 catalysts prepared by impregnation method which has excellent thermal stability and can maintain over 99 % CO selectivity even after 50 h of reaction at 600 °C. The MES method was proved to be an efficient synthesis technology for MONPs and can be extended to a variety of metal oxides catalysts.