Methane is the main component of
natural gas and shale gas. It
is chemically stable, and its activation often requires high temperatures,
which lead to its extensive transformation into undesirable products
such as CO and CO2. Thus, the development of efficient
catalysts for the selective transformation of methane represents a
substantial challenge. In this work, we synthesized La2O2CO3 samples with different morphologies (rod-
and plate-shapes) at the nanometer scale. We observed that one of
the rod-shaped samples exhibited the best catalytic properties among
the investigated samples in the oxidative coupling of methane (OCM)
at low temperatures (420–500 °C); in addition, its specific
activity was 20 times greater than that of any of the other rod-shaped
samples. This difference corresponded to the O2-TPD results
and was attributed to the crystallographic facets exposed. Among the
exposed facets, the (110), (12̅0), and (21̅0) facets had
relatively loose atomic configurations that increased the conversion
of methane in the OCM. Moreover, these facets were beneficial to the
formation of the chemisorbed oxygen species and their moderately basic
sites, which improve the selectivity in the OCM.
We present a facile
synthetic method that yields Ag@Co
x
P core–shell-type
heterogeneous nanostructures
with excellent oxygen evolution reaction (OER) activity. This nanocatalyst
can deliver a current density of 10 mA/cm2 at a small overpotential
of 310 mV and exhibits high catalytic stability. Additionally, the
catalytic activity of Ag@Co
x
P is 8 times
higher than that of the Co2P nanoparticles, owing primarily
to the strong electronic interaction between the Ag core and the Co
x
P shell.
Titanium dioxide is widely used in sunscreens because of its strong ultraviolet (UV) light absorbing capabilities and its resistance to discoloration under UV exposure. However, when deposited as a thin film, the high refractive index of titanium dioxide typically results in whiteness and opacity, which limits the use of titanium dioxide for material surfaces, for which long-term natural appearance is of high relevance. Since the whitish appearance is due to the strong light scattering and reflection on the interface of oxide particles and air, one can increase the transparency of TiO coatings by forming a continuous TiO layer. The purpose of the present article is 2-fold. First, we show that, in the presence of cerium ammonium nitrate, titanium dioxide can be turned from a white powder into a TiO/Ce xerogel via a facile bottom-up fabrication process. Second, we demonstrate that the transparent TiO/Ce xerogel can diminish surface deterioration induced by UV light and preserve the natural appearance of the highly abundant biomaterial wood. Furthermore, EPR spectroscopy revealed that the TiO/Ce xerogel coating suppresses free radical generation on wood surfaces upon UV irradiation. Our research expands the applicability of the protective effect of titanium dioxide to coatings for natural engineering materials, which will become increasingly important in future bioeconomies.
Rh sub-nano clusters supported on zeolite are remarkably more active, selective, and durable than Rh nanoparticles for the conversion of methane to syngas at low temperature.
The partial oxidation of methane is a promising method for the efficient production of syngas. To implement this process using common stainless steel reactors, an inexpensive catalyst that functions at 650°C or below is necessary. However, base metal catalysts typically require much higher temperatures, and they are deactivated by re-oxidation and coke formation. Here we report that modification of a zeolite-supported 3 wt% cobalt catalyst with a trace amount of mono-atomically dispersed rhodium (0.005 wt%) dramatically improves catalytic performance and durability. Cobalt/mordenite is nearly inactive due to the oxidation of cobalt, but the catalyst modified with rhodium continuously gives 85-86% methane conversion and 90-91% CO selectivity with an H 2 /CO ratio of 2.0 without serious coking at 650°C. During the reaction, mono-atomically dispersed rhodium converts cobalt oxide to Co 0 active species via hydrogen spillover. Use of the zeolite support is key to the high catalytic performance.
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