Scalable method for the preparation of CoxNi1-x/alumina nanocomposites and their magnetic heating properties

Magnetic nanocomposites with a high surface area matrix are attractive materials for novel catalyst supports. They can be remotely and selectively heated inside the reactor vessel when exposed to a high-frequency alternating magnetic field (AMF). These so-called "magnetic" or "cold" catalysts can revolutionize the chemical industry's electrification, particularly for renewable energy applications such as hydrogen storage and release. In this study, we developed a scalable method for synthesizing magnetic CoxNi1-x-Al2O3 nanocomposites. The synthesis is based on the co-precipitation of Co and Ni ions from an aqueous solution, coating the precipitated nanoparticles with a boehmite (AlOOH) shell via the in-situ hydrolysis of AlN powder and reduction at 850 degrees C in a flow of H-2. A combination of X-ray diffractometry (XRD) and scanning transmission electron microscopy (STEM/EDXS) showed the formation of nanocomposites containing globular CoxNi1-x nanoparticles (similar to 14 nm in size), homogenously distributed within the matrix composed of thin gamma-Al2O3 nanosheets (similar to 30 nm wide and up to 3 nm thick), providing a high specific surface area (similar to 140 m(2) g(-1)). The reduction process was studied using high-temperature XRD, hydrogen-temperature programmed reduction (H-2-TPR), and X-ray photoelectron spectroscopy (XPS). The magnetic properties were measured with a vibrating-sample magnetometer (VSM). The nanocomposites exhibited an excellent heating ability, exceeding 800 degrees C within a few minutes, even at relatively low AMF amplitudes (up to 58 mT) in a fixed-bed reactor. These results underscore the potential of CoxNi1-x-Al2O3 nanocomposites for high-temperature catalytic processes, marking an advancement in magnetic catalyst support synthesis.