Methane-to-methanol conversion over zeolite Cu-SSZ-13, and its comparison with the selective catalytic reduction of NOx with NH3†,Catalysis Science & Technology

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Methane-to-methanol conversion over zeolite Cu-SSZ-13, and its comparison with the selective catalytic reduction of NOx with NH3†
Catalysis Science & Technology ( IF 4.4 ) Pub Date : 2018-01-26 00:00:00 , DOI: 10.1039/c7cy02461d
Ramon Oord _{1,

2,

3,

4,

5} , Joel E. Schmidt _{1,

2,

3,

4,

5} , Bert M. Weckhuysen _{1,

2,

3,

4,

5}

Affiliation

The direct conversion of methane into methanol is considered as one of the holy grails in hydrocarbon chemistry and recently it was found that small pore zeolites, such as Cu-SSZ-13, Cu-SSZ-16 and Cu-SSZ-39, are active for this process. Here, we propose a reaction mechanism based on spectroscopic evidence for the methane-to-methanol reaction over Cu-SSZ-13 (Si/Al = 20). Using in situ FT-IR and operando UV-vis-NIR DRS, performed on a series of different Cu–ion-exchanged SSZ-13 zeolites, both a mono-nuclear site or a dimeric copper active site are consistent with the observations of this study. These proposed active site(s) are characterized by a ν_OH at ∼3654 cm⁻¹ and a charge transfer (CT) transition at ∼29 000 cm⁻¹. We have further evidence to complete the full catalytic cycle to methanol, including the formation of the reaction intermediate Cu(CH₃)(H₂O), which is characterized by overtone transitions, i.e., a 2ν_CH at ∼4200 cm⁻¹ and a 2ν_OH at ∼5248 cm⁻¹. We found that increasing the pre-oxidation temperature from 450 °C to 550 °C resulted in a 15% increase in methanol production, as well as a concomitant increase of the 29 000 cm⁻¹ CT transition. Furthermore, Cu-exchanged SSZ-13 zeolites, which perform well in the NH₃-SCR reaction at 200 °C (the low temperature regime), also show a high activity in the methane-to-methanol reaction and vice versa, leading us to believe that this material has a similar if not the same active site for both the catalytic reduction of NO and the stepwise reaction towards methanol.

中文翻译：

沸石Cu-SSZ-13上的甲烷制甲醇转化及其与NH ₃†选择性催化还原NO _x的比较

甲烷直接转化为甲醇被认为是烃化学领域的圣地之一，最近发现小孔沸石（如Cu-SSZ-13，Cu-SSZ-16和Cu-SSZ-39）具有活性对于这个过程。在这里，我们提出基于光谱证据的Cu-SSZ-13（Si / Al = 20）上甲烷制甲醇反应的反应机理。使用原位FT-IR和操作UV-vis-NIR DRS，对一系列不同的Cu-离子交换的SSZ-13沸石进行了分析，单核位点或二聚铜活性位点均与该观察结果一致。学习。这些提出的活性位点（一个或多个）的特征在于ν _OH在~3654厘米^-1和电荷转移（CT）在过渡〜29000厘米^-1。我们进一步证明以完成整个催化循环甲醇中，形成了包括在反应中间体的Cu（CH₃）（H₂ O），其特点是泛音过渡，即，一个2ν_CH在~4200厘米^-1和2 ν _OH在~5248厘米^-1。我们发现，将预氧化温度从450°C升高到550°C，可使甲醇产量增加15％，并伴随着29000 cm^-1 CT转变的增加。此外，在NH_3中表现良好的铜交换SSZ-13沸石-SCR反应在200°C（低温状态）下，在甲烷转化为甲醇的反应中也显示出很高的活性，反之亦然，这使我们相信这种材料对两种化合物都有相似的活性位点，即使不是相同的活性位点也是如此。催化还原NO和逐步反应生成甲醇。

更新日期：2018-01-26

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