H-ZSM-5 supported Ga (Ga/H-ZSM-5) has long been recognized as a promising catalyst for nonoxidative dehydrogenation and dehydroaromatization of alkanes. However, Ga speciation under reaction conditions remains controversial. In this work, in-situ transmission Fourier Transform infrared (FTIR) spectroscopy is employed to systematically investigate Ga speciation in Ga/H-ZSM-5 with three Si/Al ratios (15, 28 and 39) and a wide range of Ga/Al ratios (0–1.7). Quantitative FTIR spectroscopy with pyridine reveals that one Ga atom roughly replaces one Brønsted acid site (BAS) at Ga/BAS ratio up to 0.7, however, only up to ~80% of the BAS on the H-ZSM-5 can be exchanged even with excess amounts of Ga. At a low Si/Al ratio of 15, the intensity of GaH_x bands on reduced Ga/H-ZSM-5 at 550 °C increases almost linearly at low Ga loadings (Ga/Al < 0.13), and then levels off. In contrast, no detectable GaH_x bands are observed on Ga/H-ZSM-5 with a high Si/Al ratio of 39, with Ga/Al ratios up to 1.3. The dependence of GaH_x bands on both the Si/Al ratios and the Ga/Al ratios shows that Ga speciation varies with BAS density in the zeolite. We hypothesize that paired BAS sites are preferentially exchanged with Ga⁺, leading to the formation of Ga⁺−H⁺ pair sites, while the exchange of isolated BAS form isolated Ga⁺ species. Using water as a probe molecule, we show that isolated Ga⁺ and Ga⁺−H⁺ pair sites have distinct properties, i.e., the former can be easily oxidized by water at 150 °C to form GaOOH species, while the latter is inactive under the same conditions. These results provide direct experimental evidence for the existence of two types of Ga species on reduced Ga/H-ZSM-5, highlighting the possibility that they have different catalytic activities in alkane dehydrogenation reactions.

长期以来，H-ZSM-5负载的Ga（Ga / H-ZSM-5）被公认为是烷烃非氧化脱氢和脱氢芳构化的有前途的催化剂。然而，在反应条件下Ga的形成仍是有争议的。在这项工作中，采用原位透射傅立叶变换红外（FTIR）光谱系统地研究了三种Si / Al比（15、28和39）和宽范围的Ga / H-ZSM-5中的Ga形态。铝比率（0–1.7）。用吡啶进行的定量FTIR光谱分析表明，一个Ga原子可以以高达0.7的Ga / BAS比大致取代一个Brønsted酸位点（BAS），但是，即使H-ZSM-5上的BAS最多也可以交换约80％在15的低Si / Al比下，GaH _x的强度降低的Ga / H-ZSM-5在550°C时的能带在低Ga负载下（Ga / Al <0.13）几乎呈线性增加，然后趋于平稳。相比之下，在Ga / H-ZSM-5上未观察到可检测的GaH _x谱带，Si / Al比率高达39，Ga / Al比率高达1.3。GaH _x谱带对Si / Al比和Ga / Al比的依赖性表明，Ga的形成随沸石中BAS密度的变化而变化。我们假设成对的BAS位点优先与Ga ⁺交换，从而导致Ga ⁺ -H ⁺对位点的形成，而孤立的BAS的交换形成孤立的Ga ⁺物种。使用水作为探针分子，我们表明分离出的Ga ⁺和Ga ⁺ -H⁺对位点具有不同的性质，即前者可在150°C的水中轻易氧化形成GaOOH物种，而后者在相同条件下不活跃。这些结果提供了直接的实验证据，表明在还原的Ga / H-ZSM-5上存在两种类型的Ga，突出了它们在烷烃脱氢反应中具有不同催化活性的可能性。