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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >H-Bonding of Zeolite Hydroxyls with Weak Bases: FTIR Study of CO and N2 Adsorption on H-D-ZSM-5
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H-Bonding of Zeolite Hydroxyls with Weak Bases: FTIR Study of CO and N2 Adsorption on H-D-ZSM-5

机译：弱碱沸石羟基的氢键：H-D-ZSM-5吸附CO和N2的FTIR研究

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Adsorption of CO (~(13)CO) and ~(15)N2 at 100 K on H-ZSM-5 samples has been followed by FTIR spectroscopy. For better interpretation of the spectra, experiments with H-D-ZSM-5 and D-ZSM-5 were also carried out. It was established that zeolite bridging hydroxyls displaying at 100 K a band at 3616 cm~(-1) formed 1:1 adducts with CO, and as a result, the band disappeared, and two new bands at 3306 and 3415 cm~(-1) emerged at its expense. These two bands changed in concert together with a carbonyl band at 2175 cm~(-1). Experiments with H-D-ZSM-5 and D-ZSM-5 indicated that the OD band due to bridging deuteroxyls (2667 cm ) was shifted, upon CO adsorption, again to two IR bands (at 2460 and 2568 cm~(-1)). However, the shift is smaller than expected from the OH→ OD isotopic shift factor, which indicates a smaller acidity of OD groups as compared with OH. In addition, the difference in the positions of the two bands (calculated again on the basis of the isotopic shift factor), as well as their relative intensities, deviate from those observed for the OH bands. The results exclude the phenomenon to be due to heterogeneity of the bridging OH/OD groups and indicate a spectral origin. It was concluded that the appearance of two shifted bands was due to Fermi resonance with the second excitation mode of δ(OH). At high CO equilibrium pressure solvatation occurs, and the band at 3306 cm~(-1) is shifted to lower frequencies. Simultaneously, a shift of the carbonyl band to 2172 cm~(-1) was observed. At intermediate CO coverages, AlOH ··· CO complexes are also formed. It is clearly demonstrated that the CO-induced shift of the AlO—H band at 3667 cm~(-1) is ～—190 cm~(-1), and the often reported higher values are due to confusion with the 3415 cm~(-1) band described above. The AlOD groups have been found to manifest a lower acidity than that of AlOH. Here again, solvatation occurred at high CO coverages. Another effect observed at high CO coverages is the interaction of CO with silanol groups. Two kinds of interaction are unambiguously distinguished: (i) the well documented CO-induced shift of isolated silanols (3745 cm~(-1)) to 3650 cm~(-1) and (ii) a shift of silanols absorbing in the 3730—3710 cm~(-1) region to 3580 cm~(-1). No solvatation was evidenced in this case. Experiment on low temperature adsorption of ~(15)N2 confirmed that the bridging OH(OD) groups of H-ZSM-5 were homogeneous. Upon ~(15)N2 adsorption, the 3616 cm~(-1) OH band shifted by 118 cm~(-1), and the respective OD band at 2667 cm~(-1), by 81 cm~(-1). Solvatation was detected at high coverages. The ~(15)N2 induced shift of AlO—H modes was found to be 77 cm~(-1), and for AlO—D, 51 cm~(-1). Here again, two kinds of interaction with two different silanols were established. A good correlation between the shifts produced by the two probe molecules of different OH and OD groups was found.
机译：FTIR光谱分析了H​​-ZSM-5样品在100 K下吸附CO（〜（13）CO）和〜（15）N2的过程。为了更好地解释光谱，还进行了H-D-ZSM-5和D-ZSM-5的实验。结果表明，在36 K cm〜（-1）处出现100 K谱带的沸石桥连羟基与CO形成1：1的加合物，结果消失了，在3306 cm和3415 cm〜（-）出现了两个新的谱带。 1）以牺牲为代价出现了。这两个谱带与2175 cm〜（-1）的羰基谱带一致变化。使用HD-ZSM-5和D-ZSM-5进行的实验表明，在CO吸附后，由于桥联氘代羟基（2667 cm）而导致的OD波段再次移至两个IR波段（在2460和2568 cm〜（-1）处） 。然而，该位移小于从OH→OD同位素位移因子所预期的位移，这表明与OH相比，OD基团的酸度较小。此外，两个谱带位置的差异（根据同位素位移因子再次计算）以及它们的相对强度都与OH谱带所观察到的不同。结果排除了由于桥接的OH / OD基团的异质性而引起的现象，并表明了光谱的起源。结论是出现两个偏移的带是由于费米共振和δ（OH）的第二激发模。在高CO平衡压力下发生溶剂化，并且在3306 cm〜（-1）处的频带移动到较低的频率。同时，观察到羰基带向2172 cm〜（-1）移动。在中等的CO覆盖范围内，还会形成AlOH···CO络合物。清楚地表明，在3667 cm〜（-1）处，CO诱导的AlO-H谱带的位移为〜-190 cm〜（-1），而经常报道的较高值是由于与3415 cm〜之间的混淆所致。 （-1）条带。已经发现AlOD基团显示出比AlOH低的酸度。同样，在高CO覆盖率下发生溶剂化。在高CO覆盖率下观察到的另一种效果是CO与硅烷醇基团的相互作用。明确区分了两种相互作用：（i）有据可查的CO诱导的孤立硅烷醇（3745 cm〜（-1））到3650 cm〜（-1）的转变，以及（ii）3730中吸收的硅烷醇的转变-3710 cm〜（-1）到3580 cm〜（-1）。在这种情况下，没有溶剂化的迹象。 〜（15）N2的低温吸附实验证实，H-ZSM-5的桥接OH（OD）基团是均匀的。在〜（15）N2吸附后，3616 cm〜（-1）OH谱带偏移118 cm〜（-1），相应的OD谱带在2667 cm〜（-1）偏移81 cm〜（-1）。 。在高覆盖率下检测到溶剂化。发现〜（15）N2诱导的AlO-H模式位移为77 cm〜（-1），AlO-D为51 cm〜（-1）。同样，在这里建立了与两种不同硅烷醇的两种相互作用。发现不同OH和OD基团的两个探针分子产生的位移之间具有良好的相关性。

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