You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Alkane Oxidation by an Immobilized Nickel Complex Catalyst: Structural and Reactivity Differences Induced by Surface-Ligand Density on Mesoporous Silica. Immobilized nickel catalysts SBA*-L-x/Ni (L=bis(2-pyridylmethyl)(1H-1,2,3-triazol-4-ylmethyl)amine) with various ligand densities (L content (x)=0.5, 1, 2, 4 mol % Si) have been prepared from azidopropyl-functionalized mesoporous silicas SBA-N3 -x. Related homogeneous ligand L(t) (Bu) and its Ni(II) complexes, [Ni(L(t) (Bu) )(OAc)2 (H2 O)] (L(t) (Bu) /Ni) and [Ni(L(t) (Bu) )2 ]BF4 (2 L(t) (Bu) /Ni), have been synthesized. The L/Ni ratio (0.9-1.7:1) in SBA*-L-x/Ni suggests the formation of an inert [NiL2 ] site on the surface at higher ligand loadings. SBA*-L-x/Ni has been applied to the catalytic oxidation of cyclohexane with m-chloroperbenzoic acid (mCPBA). The catalyst with the lowest loading shows high activity in its initial use as the homogeneous L(t) (Bu) /Ni catalyst, with some metal leaching. As the ligand loading increases, the activity and Ni leaching are suppressed. The importance of site-density control for the development of immobilized catalysts has been demonstrated.
{"Chemical": ["[Ni(L(t) (Bu) )2 ]BF4 (2\u2009L(t) (Bu) /Ni)", "silicas", "Nickel", "Alkane", "cyclohexane", "Si", "[Ni(L(t) (Bu) )(OAc)2 (H2 O)] (L(t) (Bu) /Ni)", "NiL2", "Ni(II)", "bis(2-pyridylmethyl)(1H-1,2,3-triazol-4-ylmethyl)amine", "mCPBA", "Silica", "m-chloroperbenzoic acid", "nickel", "L(t) (Bu)", "azidopropyl", "Ni"]}