3 research outputs found
CO Oxidation on Metal Oxide Supported Single Pt atoms: The Role of the Support
Supported
metal single atoms have demonstrated excellent catalytic
performance for many chemical transformations. The effects of support
on the catalytic performance of supported single metal atoms, however,
have not been clearly elucidated. We carried out a systematic investigation
of the effects of supports on CO oxidation by single Pt (Pt<sub>1</sub>) atoms dispersed on different metal oxides: highly reducible Fe<sub>2</sub>O<sub>3</sub>, reducible ZnO, and irreducible γ-Al<sub>2</sub>O<sub>3</sub>. It was found that Pt<sub>1</sub> atoms on three
metal oxides are active for CO oxidation, and the chemical properties
of supports determine the catalytic performance of Pt<sub>1</sub> single-atom
catalysts (SACs). Both the presence of −OH groups on support
surfaces and the addition of H<sub>2</sub>O significantly modify CO
oxidation on three SACs and reduce the effects of supports on their
catalytic performances. We conclude that the interaction between single
metal atoms and support as well as surface properties of supports
control the catalytic behavior of SACs
Low-Temperature Methane Combustion over Pd/H-ZSM-5: Active Pd Sites with Specific Electronic Properties Modulated by Acidic Sites of H‑ZSM‑5
Pd/H-ZSM-5
catalysts could completely catalyze CH<sub>4</sub> to
CO<sub>2</sub> at as low as 320 °C, while there is no detectable
catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion
of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the
theoretical and experimental results prove that surface acidic sites
could facilitate the formation of active metal species as the anchoring
sites, which could further modify the electronic and coordination
structure of metal species. PdO<sub><i>x</i></sub> interacting
with the surface Brönsted acid sites of H-ZSM-5 could exhibit
Lewis acidity and lower oxidation states, as proven by the XPS, XPS
valence band, CO-DRIFTS, pyridine FT-IR, and NH<sub>3</sub>-TPD data.
Density functional theory calculations suggest PdO<sub><i>x</i></sub> groups to be the active sites for methane combustion, in the
form of [AlO<sub>2</sub>]ÂPdÂ(OH)-ZSM-5. The stronger Lewis acidity
of coordinatively unsaturated Pd and the stronger basicity of oxygen
from anchored PdO<sub><i>x</i></sub> species are two key
characteristics of the active sites ([AlO<sub>2</sub>]ÂPdÂ(OH)-ZSM-5)
for methane combustion. As a result, the PdO<sub><i>x</i></sub> species anchored by Brønsted acid sites of H-ZSM-5 exhibit
high performance for catalytic combustion of CH<sub>4</sub> over Pd/H-ZSM-5
catalysts
Revealing the Size Effect of Ceria Nanocube-Supported Platinum Nanoparticles in Complete Propane Oxidation
The
elimination of propane is one of the key tasks in
reducing
volatile organic compounds (VOCs) and automotive exhaust emissions.
The platinum nanoparticle (NP) is a promising catalyst for propane
oxidation, while the study of its structural characteristics and functionality
remains in its infancy. In this work, we synthesized the nanocubes
CeO2 with a well-defined (100) facet supporting Pt NPs
with various sizes, from 1.3 to 7 nm, and systematically investigated
the effect of the Pt size on complete propane oxidation efficiency.
In particular, CeO2(100) supported Pt NPs smaller than
4 nm promote the formation of positively charged Pt sites, which hinder
the adsorption and activation of propane and reduce the intrinsic
activity for propane oxidation. Consequently, within this size range,
the catalytic performance is primarily influenced by the electronic
state of the Pt species, with metallic Pt being identified as the
active site for the reaction. Conversely, as the particle size exceeds
4 nm, metallic Pt particles become dominant and the geometric structure
starts to influence the activity as well. Such entanglement of electronic
and geometric factors gives rise to a volcano relationship between
reaction rates and Pt particle sizes ranging from 1.3 to 7 nm, while
an increased correlation can be observed between the turnover frequencies
and the particle sizes in this range. This knowledge can guide the
synthesis of highly active catalysts, enabling the efficient oxidation
of VOCs with reduced precious metal loadings