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 Co x Ni 1-x -Al 2 O 3 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 °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 Co x Ni 1-x nanoparticles (∼ 14 nm in size), homogenously distributed within the matrix composed of thin γ-Al 2 O 3 nanosheets (∼ 30 nm wide and up to 3 nm thick), providing a high specific surface area (∼ 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 °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 Co x Ni 1-x -Al 2 O 3 nanocomposites for high-temperature catalytic processes, marking an advancement in magnetic catalyst support synthesis. • Scalable synthesis of Co x Ni 1-x -Al 2 O 3 magnetic nanocomposites was developed. • Homogeneous dispersion of Co x Ni 1-x alloyed nanoparticles (∼15 nm) in γ-Al 2 O 3 nanosheets. • Nanocomposites exhibit a high surface area (140 m 2 g −1 ) and soft magnetic properties. • Rapid heating to above 800 °C under low alternating magnetic field amplitudes. • Promising material for high-temperature catalytic processes.