Abstract
Defects are widely present in nanomaterials, and they are recognized as the active sites that tune surface properties in the local region for catalysis. Recently, the theory linking defect structures and catalytic properties of nanocatalysts has been most commonly described. In this study, we prepared boron-doped carbon nano-onions (B-CNOs) by applying an annealing treatment of ultradispersed nanodiamond particles and amorphous boron. These experimental conditions guarantee doping of CNOs with boron atoms in the entire carbon nanostructure, thereby ensuring structural homogeneity. In our research, we discuss the correlations between defective structures of B-CNOs with their catalytic properties toward SO2 and tert-butanol dehydration. We show that there is a close relationship between the catalytic properties of the B-CNOs and the experimental conditions for their formation. It is not only the mass of the substrates used for the formation of B-CNOs that is crucial, that is, the mass ratio of NDs to amorphous B, but also the process, including temperature and gas atmosphere. As it was expected, all B-CNOs demonstrated significant catalytic activity in HSO3– oxidation. However, the subsequent annealing in an air atmosphere diminished their catalytic activity. Unfortunately, no direct relationship between the catalytic activity and the presence of heteroatoms on the B-CNO surface was observed. There was a linear dependence between catalytic activity and Raman reactivity factors for each of the B-CNO materials. In contrast to SO2 oxidation, the B-CNO-a samples showed higher catalytic activity in tert-butanol dehydration due to the presence of Brønsted and Lewis acid sites. The occurence of three types of boron-Lewis sites differing in electron donor properties was confirmed using quantitative infrared spectroscopic measurements of pyridine adsorption.
Highlights
The well-defined catalysts for efficient catalytic reactions has attracted considerable interest in recent decades
Boron doping was achieved by obtaining Carbon nano-onions (CNOs) from ND in the presence of amorphous boron in a high-temperature heating process
We establish that there is a close relationship between the catalytic properties of the boron-doped carbon nano-onions (B-CNOs) and the experimental conditions for their formation
Summary
The well-defined catalysts for efficient catalytic reactions has attracted considerable interest in recent decades. The theory linking defect structures and catalytic or electrocatalytic properties of nanocatalysts has been the most commonly described one.[2,3] Defects are widely present in nanomaterials, and they are recognized as the active sites that influence catalytic properties of materials.[2,4] With regard to the dimensions, defects in solid nanomaterials can be classified into four categories:[3,4] (1) zerodimensional point defects (e.g., doping, vacancy, and reconstruction), which contain nonmetallic atom dopinginduced defects and metal defects;[2,5] (2) one-dimensional line defects (e.g., dislocation); (3) two-dimensional planar defects (e.g., grain boundaries); and (4) three-dimensional volume defects (e.g., spatial lattice disorder) These defects may be created via in situ synthesis and by the application of post-modification methods; their location in the structure is, completely different. Such behavior greatly affects the electronic properties of nanomaterials and enables optimization of chemisorption of the key intermediates which, in turn, can trigger improved catalytic performance.[6]
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