Abstract
NOx emissions in the atmosphere can cause various environmental problems, which should be strictly controlled and regulated. Furthermore, because of the limited amount of crude oil resources in the world and severe global warming, the development of fuel-efficient vehicles has long been desired. Accordingly, efficient NOx storage and reduction catalysts have been developed over the decades, called NSR (NOx storage/reduction) catalysts. In the present article, recent advances in NSR catalysts which possess ordered nanostructures will be summarized, including our noble Pt/KNO3/K-titanate nanobelt (KTN), Pt-KNO3/CeO2 and Pt-KNO3/ZrO2 catalysts, as well as nanoporous Ni-phosphate (VSB-5) and Co-substituted VSB-5 catalysts.
Highlights
Since the pioneering work of NOx storage-reduction (NSR) catalysts by Toyota’s research group, many studies have been reported on the mechanism of NSR reaction over Pt-Alkali metal (Pt)-BaO/Al2O3 catalysts
We have found that a Pt/KNO3/Ktitanate nanobelt (KTN) catalyst has the highest NOx storage capacity (2.3 mmol/g-cat) among those reported in the literature, with excellent NSR performance
We have studied the mechanism of this NSR process by kinetic measurements, in situ XRD, TEM, X-ray photoelectron spectroscopy (XPS), and FT-IR measurements during the reaction and found that the main NOx storage phase was a KNO3-like composition, which transformed into K-rich surface layers of K-titanate nanobelt- (KTN) in the reduction process
Summary
Overview of the Development on NSR Catalysts. Emissions of NOx in the atmosphere can cause various environmental problems. The conventional three-way catalyst is no longer effective for NOx removal in an oxidative atmosphere. An effective NOx removal method for lean-burn exhaust becomes desirable from the environmental and catalytic point of view. NOx removal technologies under the lean-burn condition include direct catalytic decomposition of NOx, catalytic NOx storage/reduction (NSR) [1,4,5,6,7], and selective catalytic reduction of NOx with urea/NH3 [8,9] or hydrocarbons [10,11,12]
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