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Despite significant progress in the catalytic hydrogenation of nitriles, the persistent challenge of requiring additives to prevent condensation byproducts and achieve selectivity toward primary amines demands urgent attention. In this work, we present an integrated approach utilizing a ligand-bridged Ni-Ti bimetallic complex as a precursor to tune Ni 0 -NiO-NiO(OH) heterojunctions and phases of black titania (bTiO 2 ) by controlling pyrolytic conditions. This tailored phase distribution and charge dynamics across heterojunctions create an effective balance of acidic and basic sites, enabling the direct hydrogenation of nitriles to primary amines without the need for additives. However, at elevated pyrolysis temperatures, this balanced composition begins to shift, with the loss of critical phases that alter the catalyst's structural and chemical properties. This shift reduces amphoteric behavior, resulting in decreased selectivity for primary amines and favoring the formation of condensation byproducts. The catalyst's structure, amphoteric nature, crystallinity, surface area, and active sites are comprehensively characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), temperature programmed desorption of ammonia (NH 3 -TPD), temperature programmed desorption of carbon dioxide (CO 2 -TPD), and CO 2 adsorption techniques. The magnetically retrievable catalyst exhibited excellent functional group tolerance, high selectivity, multiple reusability, broad substrate scope, and high activity for nitrile hydrogenation to primary amines, with the potential for advanced catalytic hydrogenation of other functional groups.

Transition-metal-doped black titania, primarily in the anatase phase, shows promise for redox reactions, water splitting, hydrogen generation, and organic pollutant removal, but exploring other titania phases for broader catalytic applications is underexplored. This study introduces a synthetic approach using a Co-Ti bimetallic complex bridged by a 1,10-phenanthroline-5,6-dione ligand as a precursor for the synthesis of cobalt-doped black titania [Co@L2N@b-TiO 2 ]. The synthesis involves precise control of pyrolysis conditions, yielding a distinct structure dominated by the rutile phase over anatase, with active cobalt encapsulated within a nitrogen-doped graphitic layer, primarily as Co 0 rather than Co II and Co III . The synthesized material is employed for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) under industrially viable conditions. The efficiency and selectivity of Co@L2N@b-TiO 2 was compared with other catalysts, including cobalt-doped rutile TiO 2 (Co@r-TiO 2 ), anatase TiO 2 (Co@a-TiO 2 ), and black titania (Co@b-TiO 2 ) as well as materials pyrolyzed under different atmospheres and temperatures, materials with phenanthroline ligands, and materials lacking any ligands. The superior performance of Co@L 2 N@b-TiO 2 is attributed to its high surface area, stable Co 0 within the nitrogen-doped graphitic layer, and composition of rutile and anatase phases of TiO 2 and Ti 2 O 3 (referred to as RAT), along with the synergistic interaction between RAT and Co 0 . These factors significantly influence the efficiency and selectivity of COL over hydrocinnamaldehyde (HCAL) and hydrocinnamyl alcohol (HCOL), indicating potential for broader applications beyond catalysis, particularly in designing of black titania-based materials.