Continuous syntheses of highly dispersed composite nanocatalysts via simultaneous co-precipitation in supercritical water

Abstract

Nanosized Ce0.6Zr0.3La0.05Y0.05O2−δ/γ-Al2O3(CZA) composite supports were prepared in one step using a novel continuous hydrothermal flow synthesis (CHFS) route and a conventional co-precipitation route, followed by 10h heat-treatments at 1000°C in air (to simulate accelerated ageing). HAADF STEM and HR-TEM results indicated that the sample made via CHFS route (i.e., simultaneous co-precipitation in supercritical water, denoted as sc-CZA) had homogenously dispersed CZ particles on alumina support whilst that made via conventional co-precipitation route (denoted as co-CZA sample) had a strong segregation between CZ and alumina. As a consequence of these structural and morphological properties, better sintering behaviors upon accelerated ageing and lesser grain growth of CZ particles were obtained. The sc-CZA sample was then used as supports for syntheses of three-way catalysts (TWCs), in which Pd active species were added via either directly co-precipitating (in the CHFS reactor) or simply wet impregnating Pd2+ onto the support to form composite nanocatalysts. Catalytic measurements revealed that the former had yielded a significantly higher three-way catalytic activity than the latter, attributing to its much higher dispersion of Pd species and stronger interaction between Pd and CZA support.