2 research outputs found
Efficient Metal-Free Catalytic Reaction Pathway for Selective Oxidation of Substituted Phenols
Selective oxidation of substituted
phenols to <i>p</i>-benzoquinones is known to be inefficient
because of the competing
C–O coupling reaction caused by phenoxy radicals. The poor
stability of conventional metal-based catalysts represents another
bottleneck for industrial application. Here, we describe a metal-free
reaction pathway in which onion-like carbon (OLC) as a low-cost catalyst
exhibits excellent catalytic activity and stability in the selective
oxidation of mono-, di- and trisubstituted phenols to their corresponding <i>p</i>-benzoquinones, even better than the reported metal-based
catalysts (e.g., yield, stability) and industrial catalysts for particular
substrates. Together with XPS, Raman, DFT calculations, and a series
of comparative experiments, we demonstrate that the zigzag configuration
as a type of carbon defects may play a crucial role in these reactions
by stabilizing the intermediate phenoxy radicals
Mesoporous and Graphitic Carbide-Derived Carbons as Selective and Stable Catalysts for the Dehydrogenation Reaction
Dehydrogenation
of ethylbenzene to styrene is one of the most important
catalytic processes in chemical industry. While it was demonstrated
that nanocarbons like nanotubes, nanodiamond, or nanographite show
high performance, especially selectivity, these powders give rise
to handling problems, high pressure drop, hampered heat and mass transfer,
and unclear health risks. More common macroscopic carbon materials
like activated carbons show unsatisfying selectivity below 80%. In
this study, mesoporous, graphitic, and easy to handle carbon powders
were synthesized on the basis of the reactive extraction of titanium
carbide in a novel temperature regime. This resulted in extraordinary
properties like a mean pore diameter of up to 8 nm, pore volumes of
up to 0.90 mL g<sup>–1</sup>, and graphite crystallite sizes
exceeding 25 nm. Exceptional styrene selectivities of up to 95% were
observed for materials synthesized above 1300 °C and pretreated
with nitric acid. Furthermore, the long-term stability of these non-nanocarbon
catalysts could be demonstrated for the first time during 120 h of
time-on-stream