The role of the support in Rh-based catalysts for total oxidation of CH₄ was investigated using both amorphous SiO₂ and γ-Al₂O₃ as well as ZSM-5 and SSZ-13 zeolites with varying SiO₂/Al₂O₃ ratios. The methane oxidation activity was measured in both the presence and absence of 5 vol% H₂O and 20 ppm SO₂. The support had a strong impact on Rh speciation (Rh₂O₃ nanoparticles vs. single Rh atom sites), which was important for the activity, as the nanoparticle sites were found to be far more active than the single atom sites. A 2 wt% Rh/ZSM-5(SiO₂/Al₂O₃ = 280) catalyst with Rh exclusively as Rh₂O₃ nanoparticles was able to provide oxidation at a 75 °C lower temperature than an ion-exchanged 0.294 wt% Rh/ZSM-5(SiO₂/Al₂O₃ = 30) catalyst with Rh exclusively as single atoms despite a similar concentration of active sites in the two samples. All the catalysts were inhibited by the presence of water, but this inhibition was particularly strong for an amorphous SiO₂ support and for the most Al-rich zeolites and less severe for Si-rich zeolites. The inhibition from SO₂ was relatively stronger for the more Al-rich supports, which was attributed to an uptake of sulfur at Al sites that was detrimental to the performance of the active phase. In a realistic gas atmosphere containing both H₂O and SO₂, Si-rich ZSM-5(SiO₂/Al₂O₃ = 280) therefore emerged as the best support. This was because the low acidity ensured minimal loss of Rh to the less active single atom sites, avoidance of the detrimental sulfur uptake by the support seen for more Al-rich supports, and avoidance of the strong water-induced inhibition that occurs for amorphous SiO₂ and Al-rich zeolites.

中文翻译：

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载体对铑的形态和铑基催化剂对甲烷完全氧化的催化活性的影响

在基于Rh的催化剂CH的总氧化支持体的作用，₄同时使用无定形的SiO进行了研究₂和γ-Al系₂ ö ₃以及ZSM-5和SSZ-13沸石具有不同的SiO ₂ / Al的₂ ö ₃比率。在存在和不存在5体积％的H ₂ O和20ppm的SO ₂的情况下测量甲烷的氧化活性。该载体对Rh的形态有很大影响（Rh ₂ O ₃纳米粒子与对活性很重要的单个Rh原子位点），因为发现纳米粒子的位点比单个原子位点的活性高得多。仅使用Rh作为Rh ₂ O ₃纳米粒子的2 wt％Rh / ZSM-5（SiO ₂ / Al ₂ O ₃ = 280）催化剂能够在比离子交换的0.294 wt％更低的75°C的温度下提供氧化作用Rh / ZSM-5（SiO ₂ / Al ₂ O ₃ = 30）催化剂，其中Rh仅作为单原子，尽管两个样品中的活性中心浓度相似。水的存在会抑制所有催化剂，但这种抑制作用对于无定形SiO ₂尤为强烈支持和铝含量最高的沸石和不太严重的硅含量高的沸石。对于更富铝的载体，SO ₂的抑制作用相对较强，这归因于铝位点上硫的吸收，这对活性相的性能有害。因此，在包含H ₂ O和SO ₂的实际气体气氛中，富含Si的ZSM-5（SiO ₂ / Al ₂ O ₃ = 280）成为最好的载体。这是因为低酸度可确保Rh减少至活性较低的单原子位点，从而避免了Rh的最小损失，避免了富铝载体更多的载体对有害硫的吸收，并且避免了无定形SiO对水的强烈抑制作用₂ 和富含铝的沸石。