Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
296
result(s) for
"Huang, Weixin"
Sort by:
Enhancing both selectivity and coking-resistance of a single-atom Pd1/C3N4 catalyst for acetylene hydrogenation
Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride （g-C3N4） using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy （HAADF-STEM） confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle （NP） formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.
Journal Article
The active sites of Cu–ZnO catalysts for water gas shift and CO hydrogenation reactions
Cu–ZnO–Al
2
O
3
catalysts are used as the industrial catalysts for water gas shift (WGS) and CO hydrogenation to methanol reactions. Herein, via a comprehensive experimental and theoretical calculation study of a series of ZnO/Cu nanocrystals inverse catalysts with well-defined Cu structures, we report that the ZnO–Cu catalysts undergo Cu structure-dependent and reaction-sensitive in situ restructuring during WGS and CO hydrogenation reactions under typical reaction conditions, forming the active sites of Cu
Cu(100)
-hydroxylated ZnO ensemble and Cu
Cu(611)
Zn alloy, respectively. These results provide insights into the active sites of Cu–ZnO catalysts for the WGS and CO hydrogenation reactions and reveal the Cu structural effects, and offer the feasible guideline for optimizing the structures of Cu–ZnO–Al
2
O
3
catalysts.
Identification of active sites of a catalyst is the Holy Grail in heterogeneous catalysis. Here, the authors successfully identify the Cu
Cu(100)
- hydroxylated ZnO ensemble and Cu
Cu(611)
Zn alloy as the active sites of Cu-ZnO catalysts for water gas shift and CO hydrogenation reactions, respectively.
Journal Article
Memory-dictated dynamics of single-atom Pt on CeO2 for CO oxidation
Single atoms of platinum group metals on CeO
2
represent a potential approach to lower precious metal requirements for automobile exhaust treatment catalysts. Here we show the dynamic evolution of two types of single-atom Pt (Pt
1
) on CeO
2
, i.e., adsorbed Pt
1
in Pt/CeO
2
and square planar Pt
1
in Pt
AT
CeO
2
, fabricated at 500 °C and by atom-trapping method at 800 °C, respectively. Adsorbed Pt
1
in Pt/CeO
2
is mobile with the in situ formation of few-atom Pt clusters during CO oxidation, contributing to high reactivity with near-zero reaction order in CO. In contrast, square planar Pt
1
in Pt
AT
CeO
2
is strongly anchored to the support during CO oxidation leading to relatively low reactivity with a positive reaction order in CO. Reduction of both Pt/CeO
2
and Pt
AT
CeO
2
in CO transforms Pt
1
to Pt nanoparticles. However, both catalysts retain the memory of their initial Pt
1
state after reoxidative treatments, which illustrates the importance of the initial single-atom structure in practical applications.
The use of single atoms of platinum group metals on CeO
2
is a promising approach to reduce precious metal requirements for automobile exhaust treatment catalysts. Here, the authors discovered that by manipulating the calcination temperatures, they could control the configuration of Pt1 on the CeO
2
surface, leading to differences in CO oxidation activity.
Journal Article
Molecular oxygen enhances H2O2 utilization for the photocatalytic conversion of methane to liquid-phase oxygenates
H
2
O
2
is widely used as an oxidant for photocatalytic methane conversion to value-added chemicals over oxide-based photocatalysts under mild conditions, but suffers from low utilization efficiencies. Herein, we report that O
2
is an efficient molecular additive to enhance the utilization efficiency of H
2
O
2
by suppressing H
2
O
2
adsorption on oxides and consequent photogenerated holes-mediated H
2
O
2
dissociation into O
2
. In photocatalytic methane conversion over an anatase TiO
2
nanocrystals predominantly enclosed by the {001} facets (denoted as TiO
2
{001})-C
3
N
4
composite photocatalyst at room temperature and ambient pressure, O
2
additive significantly enhances the utilization efficiency of H
2
O
2
up to 93.3%, giving formic acid and liquid-phase oxygenates selectivities respectively of 69.8% and 97% and a formic acid yield of 486 μmol
HCOOH
·g
catalyst
−1
·h
−1
. Efficient charge separation within TiO
2
{001}-C
3
N
4
heterojunctions, photogenerated holes-mediated activation of CH
4
into ·CH
3
radicals on TiO
2
{001} and photogenerated electrons-mediated activation of H
2
O
2
into ·OOH radicals on C
3
N
4
, and preferential dissociative adsorption of methanol on TiO
2
{001} are responsible for the active and selective photocatalytic conversion of methane to formic acid over TiO
2
{001}-C
3
N
4
composite photocatalyst.
The oxidation of methane to formic acid or related oxygenates relies on efficient reaction with H
2
O
2
. Here, the authors report a TiO
2
-based catalyst to selectively form formic acid by using molecular O
2
additives to avoid unwanted side reactions.
Journal Article
PdCu nanoalloy decorated photocatalysts for efficient and selective oxidative coupling of methane in flow reactors
Methane activation by photocatalysis is one of the promising sustainable technologies for chemical synthesis. However, the current efficiency and stability of the process are moderate. Herein, a PdCu nanoalloy (~2.3 nm) was decorated on TiO
2
, which works for the efficient, stable, and selective photocatalytic oxidative coupling of methane at room temperature. A high methane conversion rate of 2480 μmol g
−1
h
−1
to C
2
with an apparent quantum efficiency of ~8.4% has been achieved. More importantly, the photocatalyst exhibits the turnover frequency and turnover number of 116 h
−1
and 12,642 with respect to PdCu, representing a record among all the photocatalytic processes (λ > 300 nm) operated at room temperature, together with a long stability of over 112 hours. The nanoalloy works as a hole acceptor, in which Pd softens and weakens C-H bond in methane and Cu decreases the adsorption energy of C
2
products, leading to the high efficiency and long-time stability.
Efficient and stable photocatalytic oxidative coupling of methane to C2 products is revealed by Tang’s group via synergistic effects of a PdCu nanoalloy cocatalyst which achieves high TON
PdCu
of 12642 and TOF
PdCu
of 116 h
−1
with >100 hour stability.
Journal Article
Single rhodium atoms anchored in micropores for efficient transformation of methane under mild conditions
Catalytic transformation of CH
4
under a mild condition is significant for efficient utilization of shale gas under the circumstance of switching raw materials of chemical industries to shale gas. Here, we report the transformation of CH
4
to acetic acid and methanol through coupling of CH
4
, CO and O
2
on single-site Rh
1
O
5
anchored in microporous aluminosilicates in solution at ≤150 °C. The activity of these singly dispersed precious metal sites for production of organic oxygenates can reach about 0.10 acetic acid molecules on a Rh
1
O
5
site per second at 150 °C with a selectivity of ~70% for production of acetic acid. It is higher than the activity of free Rh cations by >1000 times. Computational studies suggest that the first C–H bond of CH
4
is activated by Rh
1
O
5
anchored on the wall of micropores of ZSM-5; the formed CH
3
then couples with CO and OH, to produce acetic acid over a low activation barrier.
Catalytic transformation of CH
4
under mild conditions has implications to shale gas utilization. Here, the authors report the transformation of CH
4
to acetic acid through coupling of CH
4
, CO and O
2
on single-site Rh
1
O
5
anchored in microporous aluminosilicates in liquid phase.
Journal Article
Quantification of critical particle distance for mitigating catalyst sintering
Supported metal nanoparticles are of universal importance in many industrial catalytic processes. Unfortunately, deactivation of supported metal catalysts via thermally induced sintering is a major concern especially for high-temperature reactions. Here, we demonstrate that the particle distance as an inherent parameter plays a pivotal role in catalyst sintering. We employ carbon black supported platinum for the model study, in which the particle distance is well controlled by changing platinum loading and carbon black supports with varied surface areas. Accordingly, we quantify a critical particle distance of platinum nanoparticles on carbon supports, over which the sintering can be mitigated greatly up to 900 °C. Based on in-situ aberration-corrected high-angle annular dark-field scanning transmission electron and theoretical studies, we find that enlarging particle distance to over the critical distance suppress the particle coalescence, and the critical particle distance itself depends sensitively on the strength of metal-support interactions.
Deactivation of supported metal catalysts via thermally induced sintering is a major concern in the catalysis community. Here, the authors demonstrate that enlarging particle distance to over the critical distance could suppress the particle coalescence greatly up to 900 °C.
Journal Article
The most active Cu facet for low-temperature water gas shift reaction
Identification of the active site is important in developing rational design strategies for solid catalysts but is seriously blocked by their structural complexity. Here, we use uniform Cu nanocrystals synthesized by a morphology-preserved reduction of corresponding uniform Cu
2
O nanocrystals in order to identify the most active Cu facet for low-temperature water gas shift (WGS) reaction. Cu cubes enclosed with {100} facets are very active in catalyzing the WGS reaction up to 548 K while Cu octahedra enclosed with {111} facets are inactive. The Cu–Cu suboxide (Cu
x
O,
x
≥ 10) interface of Cu(100) surface is the active site on which all elementary surface reactions within the catalytic cycle proceed smoothly. However, the formate intermediate was found stable at the Cu–Cu
x
O interface of Cu(111) surface with consequent accumulation and poisoning of the surface at low temperatures. Thereafter, Cu cubes-supported ZnO catalysts are successfully developed with extremely high activity in low-temperature WGS reaction.
Nanocrystals display a variety of facets with different catalytic activity. Here the authors identify the most active facet of copper nanocrystals relevant to the low-temperature water gas shift reaction and further design zinc oxide-copper nanocubes with exceptionally high catalytic activity.
Journal Article
Understanding complete oxidation of methane on spinel oxides at a molecular level
It is crucial to develop a catalyst made of earth-abundant elements highly active for a complete oxidation of methane at a relatively low temperature. NiCo
2
O
4
consisting of earth-abundant elements which can completely oxidize methane in the temperature range of 350–550 °C. Being a cost-effective catalyst, NiCo
2
O
4
exhibits activity higher than precious-metal-based catalysts. Here we report that the higher catalytic activity at the relatively low temperature results from the integration of nickel cations, cobalt cations and surface lattice oxygen atoms/oxygen vacancies at the atomic scale.
In situ
studies of complete oxidation of methane on NiCo
2
O
4
and theoretical simulations show that methane dissociates to methyl on nickel cations and then couple with surface lattice oxygen atoms to form –CH
3
O with a following dehydrogenation to −CH
2
O; a following oxidative dehydrogenation forms CHO; CHO is transformed to product molecules through two different sub-pathways including dehydrogenation of OCHO and CO oxidation.
The development of methane oxidation catalysts made of earth-abundant elements is an important challenge. Here, the authors report a cost-effective nickel-cobalt oxide which outperforms precious-metal-based alternatives, due to the combination of transition metal cations and surface oxygen vacancies.
Journal Article