The dehydroaromatization (DHA) reaction of methane under non-oxidative conditions is carried out over a molybdenum catalyst supported on HZSM-5 and boric acid (BA) treated HZSM-5 at 700 °C and atmospheric pressure. As compared to the conventional Mo/HZSM-5 catalyst, wherein a maximum of 100 nmol g_cat⁻¹ s⁻¹ of benzene is measured, BA treated Mo/HZSM-5 exhibited a significantly high benzene formation rate (∼420 nmol g_cat⁻¹ s⁻¹) at around 90 minutes time on stream. In addition, a boron treated catalyst was measured to have an 8 wt% reduction in coke formation as compared to the untreated catalyst. One prevailing thought for improved activity is ascribed to the desired moderation of Brønsted acid sites on BA treatment. This is probed by temperature programmed desorption (TPD) experiments which indicated an overall reduction in Brønsted acidity on BA treatment of the catalyst. Quantum mechanical density functional theory (DFT) calculations further estimated a high deprotonation energy (DPE) of the Brønsted acidic proton anchored on the boron substituted site (DPE = 1145.4 kJ mol⁻¹) as compared to the Al site (DPE = 1100.6 kJ mol⁻¹) of the zeolite framework, suggesting a reduction in Brønsted acidity. FTIR and ¹¹B MAS NMR spectra confirmed the presence of trigonal boron species substituted in the zeolite framework. In addition, the molybdenum oxide (Mo⁶⁺) species, which is known to act as the precursor for active sites in methane DHA, is observed to form in a relatively greater quantity on the boron treated catalyst in the temperature program reduction (TPR) study of the calcined catalysts. Thus, BA treatment moderates the acidity of the Mo/HZSM-5 catalyst to provide the desired active sites for high reactivity.

中文翻译：

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硼酸处理过的HZSM-5可改善非氧化甲烷脱氢芳构化中的催化剂活性

甲烷在非氧化条件下的脱氢芳香化（DHA）反应在负载于HZSM-5的钼催化剂和硼酸（BA）处理的HZSM-5上于700°C和大气压下进行。与传统的Mo / HZSM-5催化剂相比，苯的最大测量值为100 nmol g _cat ^-1 s ^-1，与BA处理的Mo / HZSM-5相比，苯的形成率非常高（〜420 nmol g _cat ^-1 s ^-1）-1秒^-1）播放约90分钟。另外，经测量，与未处理的催化剂相比，经硼处理的催化剂的焦炭形成减少了8重量％。改善活性的一种普遍想法归因于BA处理中布朗斯台德酸位点的理想缓和作用。这是通过程序升温脱附（TPD）实验进行的，该实验表明在BA处理催化剂后布朗斯台德酸度总体下降。量子力学密度泛函理论（DFT）计算进一步估计了锚定在硼取代位点（DPE = 1145.4 kJ mol ^-1）上的Brønsted酸性质子与Al位点（DPE = 1100.6 kJ mol ）的高去质子能（DPE）^-1）的分子筛，这表明布朗斯台德酸度降低。FTIR和¹¹ B MAS NMR光谱证实了沸石骨架中存在取代的三角硼物种。此外，在温度程序还原（TPR）中，观察到氧化钼（Mo ⁶⁺）物种在甲烷处理的DHA中的活性位点上相对较多地形成，这是众所周知的。煅烧催化剂的研究。因此，BA处理降低了Mo / HZSM-5催化剂的酸度，以提供所需的高反应活性位点。