Pt and Pd supported on beta zeolites, with different silica to alumina ratios (SARs), are examined in the form of diesel oxidation catalysts (DOCs) for the oxidation of CO, NO, C₃H₈, and C₃H₆. The effect of SARs on the physicochemical properties of the catalysts, their subsequent oxidation activity, and sulfur tolerance was investigated. A beta zeolite with a high SAR has low acidity and high hydrophobicity, which induces the agglomeration of either Pt or Pd in the catalysts during preparation and thermal treatment. The effect of sintering is more severe on Pt than on Pd catalysts. High-SAR zeolites retained Pt in a more metallic fraction in the obtained catalysts, whereas this effect was not significant for the Pd-based catalyst, wherein Pd exists mostly in the oxide form. High-SAR Pt/BEA and Pd/BEA catalysts exhibit better conversion of CO, NO, C₃H₈, and C₃H₆ than low-SAR catalysts. A linear relationship for turnover frequency (TOF) with SAR (and with average particle size) was found for all four oxidation reactions, namely, the higher is the SAR, the higher is the TOF. This suggests that the catalysts are tailorable by adjusting the SAR of the zeolite supports. A five-cycle test indicated that zeolite-based catalysts have greater stability than alumina-based catalysts. The activity for NO oxidation was very stable for the high-silicious Pt/BEA catalyst with time-on-stream, which was not the case for the Pt/Al₂O₃ catalyst. The Pd/BEA catalysts were more susceptible to sulfur poisoning than their Pt counterparts; however, they were easily regenerated. Also, the Pt/BEA catalysts were effectively regenerated, especially for the highest SAR.

中文翻译：

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Si/Al比对β沸石负载的Pt和Pd作为柴油氧化催化剂的氧化和耐硫性能的影响

以柴油氧化催化剂 (DOC) 的形式研究了负载在具有不同二氧化硅与氧化铝比 (SAR) 的 β 沸石上的 Pt 和 Pd，用于氧化 CO、NO、C ₃ H ₈和 C ₃ H ₆. 研究了 SAR 对催化剂的物理化学性质、随后的氧化活性和耐硫性的影响。具有高 SAR 的 β 沸石具有低酸性和高疏水性，这会在制备和热处理过程中引起催化剂中 Pt 或 Pd 的团聚。烧结对 Pt 的影响比对 Pd 催化剂的影响更大。高 SAR 沸石在获得的催化剂中保留了更多金属部分的 Pt，而这种效果对于 Pd 基催化剂并不显着，其中 Pd 主要以氧化物形式存在。高 SAR Pt/BEA 和 Pd/BEA 催化剂表现出更好的 CO、NO、C ₃ H ₈和 C ₃ H _6转化率低于低 SAR 催化剂。对于所有四种氧化反应，均发现转换频率 (TOF) 与 SAR（以及平均粒径）呈线性关系，即 SAR 越高，TOF 越高。这表明可以通过调节沸石载体的 SAR 来调整催化剂。五循环测试表明，沸石基催化剂比氧化铝基催化剂具有更高的稳定性。对于具有运行时间的高硅Pt/BEA催化剂，NO氧化活性非常稳定，而Pt/Al ₂ O ₃催化剂则不然。Pd/BEA 催化剂比 Pt 催化剂更容易发生硫中毒；但是，它们很容易再生。此外，Pt/BEA 催化剂得到了有效再生，特别是对于最高 SAR。