Linking the Defective Structure of Boron-Doped Carbon Nano-Onions with Their Catalytic Properties: Experimental and Theoretical Studies

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 SO 2 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 HSO 3 – 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 SO 2 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.

Construction of Boron‐ and Nitrogen‐Enriched Nanoporous π‐Conjugated Networks Towards Enhanced Hydrogen Activation

“…The results Figure 2. A) TGA results of the HAT(CN) 6 monomer and the mixture of HAT(CN) 6 /NaBH 4 (mass ratio of 1 : 1) from 25 to 800 °C with a ramping rate of 10 °C min À 1 ; B) N 2 isotherms (77 K) of BN-NCN-T (values are offset along the y-axis by 50 cm 3 g À 1 (BN-NCN-650), 200 cm 3 g À 1 (BN-NCN-750), 350 cm 3 g À 1 (BN-NCN-850)); C) Pore size distribution curves of BN-NCN-T (values are offset along the y-axis by 0.68 cm 3 g À 1 nm À 1 (BN-NCN-650), 1.60 cm 3 g À 1 nm À 1 (BN-NCN-750), 2.48 cm 3 g À 1 nm À 1 (BN-NCN-850)); D) Raman spectra; E) FTIR; F) Solid-state 13 C NMR; G) Solid-state 11 B NMR of BN-NCN-T; H) Content of B and N in BN-NCN-T being obtained from XPS analysis and elemental analysis; I) B1s, N1s, and C1s XPS spectra of BN-NCN-750; J) SEM and K) TEM images of BN-NCN-750.…”

“…Treatment of the mixture at 100 °C for 12 h led to the formation of HD, as shown by the newly formed triplet peaks, with a H 2 : HD ratio of 1 : 0.39. The amount of the produced HD was gradually accumulated while the reaction time was prolonged, with a H 2 : HD ratio of 1 : 0.45 being achieved after 48 h. Operando solid state 11 B NMR was conducted to study the evolution of B sites at temperatures of 120, 200 and 250 °C. In the fresh BN-NCN-750 scaffolds, B signals are mainly composed of three-coordinated B sites (e.g., BN 3 ) and BÀ C bond.…”

“…In addition, B-doping could manipulate the electronic properties and charge flows within the nanocatalyst scaffolds and tune the corresponding catalytic activity. Current approaches capable of introducing Binvolved species within the nanomaterials mainly included (Table S1): (1) construction of nanoporous frameworks (e.g., metal organic frameworks (MOFs)) deploying Bcontaining monomers; [9] (2) chemical vapor deposition (CVD) method using volatile B-containing precursors (e.g., triphenylborane); [8] (3) In situ doping pathway via carbonization in the presence of B-containing precursors (e.g., boric acid); [4,10] (4) Post-modification of carbon materials via high temperature treatment in the presence of B-containing sources (e.g., boron, [11] boric acid, [3] boron oxide, [7] ionic liquid (IL) with tetrafluoroborate anion (BF 4 À ), [1,12] and NaBH 4 [6] ). However, the tedious synthesis procedure of the B-containing monomers in pathway (1), in which repeated protection/deprotection was required due to the high reactivity of the B sites, and the small quantity being afforded by each batch in pathway (2) limited their practical applications.…”

“…Upon the increase in the treatment temperature, the hump around 130 ppm, attributed to the aromatic carbons in the internal ring, decreased, indicating partial decomposition of the architectures. The structural evolutions of the BN-NCN-T products are more clearly visible in the11 B DPMASAngewandte Chemie Forschungsartikel spectra (Figure…”

“…and11 B direct polarization magic-angle spinning (DPMAS) NMR spectra were collected to provide further structural information. The 13 C DPMAS spectra showed a single, broad signal spanning between 110 and 140 ppm (Figure2F), being assigned to the aromatic carbon signals.…”