TOPICS IN CATALYSIS
·
2024
·
IF 2.8
Wang Xinyu,Xu Xin,Xiong Wuwan,Ye Daiqi,Chen Peirong
Catalytic oxidation is an effective solution for the control of methane (CH 4 ) emission in exhausts from natural gas vehicles. Pd-based small-pore zeolites (such as Pd-SSZ-13) are considered to be the most active catalysts for CH 4 oxidation, but H 2 O in the exhausts tends to induce deactivation of Pd catalysts. In this work, we tuned the hydrophobicity of Pd-SSZ-13 as a representative to improve its H 2 O resistance in CH 4 oxidation. Pd-SSZ-13 catalysts with different Si/Al ratios were obtained by dealuminizing the pristine SSZ-13 zeolite with acid followed by Pd ion exchange, and a reduction of T 50 (i.e. the temperature to reach 50% conversion of CH 4 ) by 20 ℃ was achieved in CH 4 oxidation in the presence of 10 vol.% H 2 O. Detailed physicochemical characterizations showed that the fraction of highly dispersed PdO species (highly active in CH 4 oxidation) increased, whereas that of less inactive PdO x clusters decreased, in the Pd-SSZ-13 after acid modification. In addition, the increase of zeolite hydrophobicity after acid modification alleviated the H 2 O inhibition effect on the active PdO phase, leading to a less activity loss of Pd-SSZ-13 in CH 4 oxidation. The improved hydrophobicity also favored C 3 H 8 combustion over Pd-SSZ-13. These results suggested that simple acid modification could tune effectively the Si/Al ratio and hydrophobicity of zeolite supports, and eventually the physicochemical properties and oxidation performance of the supported Pd catalysts.
研究领域:
催化化学
·
环境科学
✓ 已验证
DOI
高影响因子
ACS Catalysis
·
2021
·
IF 13.084
Dongdong Chen,Huarong Lei,Wuwan Xiong,Ying Li,Xiang Ji,Jia-Yue Yang,Baoxiang Peng,Mingli Fu,Peirong Chen,Daiqi Ye
Phosphorus (P) originating from lubricant oil additives or biofuels is an emerging chemical poison in catalytic systems for automotive exhaust after-treatment. Here, we demonstrate that P-poisoning led to severe deactivation of small-pore Pd-SSZ-13 zeolites (with CHA framework) as passive NOx adsorbers (PNA) and CO oxidation catalysts for cold-start exhaust purification applications. Deactivation mechanisms of P-poisoning were unraveled by comparatively examining the P-free and P-loaded Pd-SSZ-13 zeolites using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), temperature-programmed reduction by hydrogen (H2-TPR), CO pulse adsorption, temperature-programmed desorption using NH3 as a probe molecule (NH3-TPD), ultraviolet/visible light (UV/vis) spectroscopy, and in situ diffuse relectance infrared Fourier transform spectroscopy (DRIFTS). The loss of isolated Pd sites─namely, [Pd(OH)]+ and Pd2+ (located in the eight- and six-membered rings of CHA framework, respectively)─was revealed to be largely responsible for the deactivation of Pd-SSZ-13 in passive NOx adsorption and catalytic CO oxidation. In situ DRIFTS studies using NO or CO as a probe molecule suggest that [Pd(OH)]+ was more susceptible to P-poisoning than Pd2+. Specifically, P-poisoning led to a migration of [Pd(OH)]+ from cationic exchange sites to the zeolite surface, forming inactive metaphosphate (i.e., [Pd(OH)]+PO3–) and bulk PdOx species at high temperatures. In contrast, P-poisoning of Pd2+ sites proceeded via a sequential transformation to [Pd(OH)]+ first, and then to [Pd(OH)]+PO3– and bulk PdOx. This study provides a comprehensive mechanistic understanding on the deactivation of Pd-SSZ-13 by P-poisoning, and may guide the design of high-performance, phosphorus-resistant Pd-zeolite catalysts for cold-start exhaust after-treatment.
研究领域:
催化材料
·
环境科学
·
化学工程
✓ 已验证
DOI
高影响因子
FUEL
·
2023
·
IF 7.4
Yinan Wang,Xuteng Zhao,Ting Chen,Zuwei Zheng,Rijing Zhan,He Lin
Pd/SSZ-13 with different Al distributions were hydrothermally synthesized and utilized as passive NOx adsorbers (PNA). The characterization results indicated that more concentrated Al distribution can not only improve the ion-exchanged level of Pd but also generated more Z 2 Pd 2+ sites at six-member rings. Thus, as revealed by NOx adsorption experiments, samples with more Z 2 Pd 2+ sites showed high NOx storage capacity as well as stronger water resistance. Besides, 84.8 % adsorption capacity of this sample was retained after hydrothermal aging treatment. On the other side, Pd existed as [Pd(OH)] + sites on SSZ-13 with isolated Al as the majority. These sites were vulnerable to H 2 O and less stable. Seriously Pd agglomerated was observed on the aged Pd/SSZ-13 with less paired Al. This study revealed that proper Al distribution on SSZ-13 could significantly improve the performance and stability of the catalyst and provided a new direction for the design of PNA catalysts.
研究领域:
催化化学
·
环境科学
✓ 已验证
DOI
高影响因子
RSC Advances
·
2026
·Vol. 16
·期 1
·383-393
·
IF 4.6
Dongdong Chen,Weiqi Zhang,Zhenzhen Jia,Huibin Liu,Bo Zhang,Shasha Liu,Feng Liang,Wuwan Xiong,Xiang Li
Pd-loaded CHA zeolites (e.g., Pd-SSZ-13) have been identified as a promising candidate for passive NOx adsorption (PNA) in low-temperature environments. The inclusion of lubricant oil additives or biofuels in automotive exhaust after-treatment systems subjects Pd-SSZ-13 to chemical poisoning from contaminants such as alkali metals (e.g., Na and K). In this study, we present a straightforward yet highly effective approach to regenerate Pd-SSZ-13 that has been poisoned by alkali metals, achieved through washing with a dilute NH4Cl solution. The underlying mechanisms of both poisoning and regeneration were thoroughly explored, revealing that the deactivation due to alkali-metal poisoning is primarily attributed to the transformation of the active Pd2+ ion into PdOx and a concomitant reduction in Brønsted acid sites. The NH4Cl washing not only removes alkali metal contaminants, thereby restoring the Brønsted acid sites previously occupied by them, but also converts the inert PdOx back into their active states (i.e., isolated Pd2+). This investigation unveils a simplified yet highly efficient NH4Cl washing technique for the regeneration of the deactivated Pd-SSZ-13, offering profound implications for extending the catalyst's lifespan and enhancing its performance in cold-start exhaust after-treatment applications.
✓ 已验证
产品关联
DOI
PubMed
高影响因子
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
·
2026
·
IF 5.4
Dongdong Chen,Siting Hu,Zhenzhen Jia,Huibin Liu,Bo Zhang,Shasha Liu,Wuwan Xiong,Xiang Li
The integration of lubricant oil additives or biofuels compels the Passive NO x Adsorber (PNA) within automotive exhaust after-treatment systems to withstand chemical poisoning from contaminants such as phosphorus (P). For the first time, lanthanum (La) has been employed to enhance the operational efficacy of Pd-loaded small-pore SSZ-13 zeolite (i.e., Pd-SSZ-13) in the presence of phosphorus species. Our findings reveal that La modification significantly bolsters the resilience of Pd-SSZ-13 against P-induced deactivation during the cold-start phase. Furthermore, we have elucidated a pronounced reduction in the degradation of active cationic Pd 2 + ions and Brønsted acid sites within the Pd-SSZ-13 framework upon the introduction of La. Notably, La not only exerts a stabilizing influence on the framework aluminum at the Brønsted acid sites but also effectively mitigates the interaction between the active Pd 2+ species and phosphorus, thereby preventing the formation of metaphosphate and its subsequent conversion into bulk PdO x aggregates. This research offers profound insights, particularly concerning the utilization of La to augment the resistance of Pd-SSZ-13 zeolite catalysts against poisoning by various chemical poisons (such as alkali metals or sulfur) and to enhance their high-temperature hydrothermal stability.
✓ 已验证
产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）