Activation of Pd/SSZ-13 catalyst by hydrothermal aging treatment in passive NO adsorption performance at low temperature for cold start application

Future emission standards are becoming increasingly stringent. Around 50% of targeted tailpipe emissions are emitted during the cold-start period, mainly due to the ineffectiveness of catalytic converters in the after-treatment...

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The Hydrothermal Stability and the Properties of Non- and Strongly-Interacting Rh Species over Rh/γ, θ-Al2O3 Catalysts

Catalysts ◽

10.3390/catal11010099 ◽

2021 ◽

Vol 11 (1) ◽

pp. 99

Author(s):

Guanghao Cheng ◽

Gurong Shen ◽

Jun Wang ◽

Yunhao Wang ◽

Weibo Zhang ◽

...

Keyword(s):

Activation Energy ◽

Apparent Activation Energy ◽

Aging Time ◽

Reaction Path ◽

Aging Treatment ◽

Hydrothermal Stability ◽

Hydrothermal Aging ◽

Strongly Interacting

The present work reports the effects of γ-, θ-phase of alumina on the hydrothermal stability and the properties of non- and strongly-interacting Rh species of the Rh/Al2O3 catalysts. Comparing to γ-Al2O3, θ-Al2O3 can not only reduce the amount of occluded Rh but also better stabilize Rh during hydrothermal aging treatment. When the aging time was prolonged to 70 h, all the non-interacting Rh was transformed into strongly-interacting Rh and occluded Rh. The XPS results indicated that non- and strongly-interacting Rh might exist in the form of Rh/Rh3+ and Rh4+, respectively. CO-NO reaction was chosen as a probe reaction to research more information about non- and strongly-interacting Rh. The two Rh species had similar apparent activation energy (Eapp) of 170 kJ/mol, which indicated that non- and strongly-interacting Rh follow the same reaction path. The non-interacting Rh was removed from aged samples by the acid-treated method, and obtained results showed that only 2.5% and 4.0% non-interacting Rh was maintained in aged Rh/γ-Al2O3 and Rh/θ-Al2O3.

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Pd/FER vs Pd/SSZ-13 Passive NOx Adsorbers: Adsorbate-controlled Location of Atomically Dispersed Pd(II) in FER Determines High Activity and Stability

10.26434/chemrxiv.12385577 ◽

2020 ◽

Author(s):

Konstantin Khivantsev ◽

Xinyi Wei ◽

Libor Kovarik ◽

Nicholas R. Jaegers ◽

Eric D. Walter ◽

...

Keyword(s):

Low Temperature ◽

Beneficial Effect ◽

Hot Spots ◽

Release Behavior ◽

Hydrothermal Aging ◽

Practical Applications ◽

Systematic Exploration ◽

No Release ◽

Co Concentration ◽

Very High

Pd-loaded FER and SSZ-13 zeolites as low-temperature passive NOx adsorbers (PNA) are compared under practically relevant conditions. Vehicle cold-start exposes the material to CO under a range of concentrations, necessitating a systematic exploration of the effect of CO on the performance of isolated Pd ions for PNA. NO release temperature of both adsorbers decreases gradually with the increase of CO concentration from a few hundred to a few thousand ppm. This beneficial effect results from local nano-“hot spots” formation during CO oxidation. Dissimilar to Pd/SSZ-13, increasing the CO concentration above ~1,000 ppm improves the NOx storage significantly for Pd/FER, attributed to the presence of a Pd ions in FER γ-site that is shielded from NOx. CO mobilizes this Pd atom to the NOx accessible position where it becomes active for PNA. This behavior explains the very high resistance of Pd/FER to hydrothermal aging: Pd/FER materials survive hydrothermal aging at 800⁰C in 10% H2O vapor for 16 hours with no deterioration in NOx uptake/release behavior. Thus, by allocating Pd ions to the specific microporous pockets in FER, we have produced very hydrothermally stable and active PNA materials with immediate practical applications.

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