Feyel Sandra, Scharfenberg Ludwig, Daniel Charles, Hartl Hans, Schröder Detlef, Schwarz Helmut
Institut für Chemie der Technischen Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany.
J Phys Chem A. 2007 May 3;111(17):3278-86. doi: 10.1021/jp067454o. Epub 2007 Apr 6.
Bare vanadium oxide and hydroxide cluster cations, V(m)O(n)+ and V(m)O(n-1) (OH)+ (m = 1-4, n = 1-10), generated by electrospray ionization, were investigated with respect to their reactivity toward methanol using mass spectrometric techniques. Several reaction channels were observed, such as abstraction of a hydrogen atom, a methyl radical, or a hydroxymethyl radical, elimination of methane, and adduct formation. Moreover, dehydrogenation of methanol to generate formaldehyde was found to occur via four different pathways. Formaldehyde was released as a free molecule either upon transfer of two hydrogen atoms to the cluster or upon transfer of an oxygen atom from the cluster to the neutral alcohol concomitant with elimination of water. Further, formaldehyde was attached to V(m)O(n)+ upon loss of H2 or neutral water to produce the cation V(m)O(n)(OCH(2))+ or V(m)O(n-1) (OCH(2))+, respectively. A reactivity screening revealed that only high-valent vanadium oxide clusters are reactive with respect to H2 uptake, oxygen transfer, and elimination of H2O, whereas smaller and low-valent cluster cations are capable of dehydrogenating methanol via elimination of H2. For comparison, the reactivity of methanol with the corresponding hydroxide cluster ions, V(m)O(n-1) (OH)+, was studied also, for which dominant pathways lead to both condensation and association products, i.e., generation of the ions V(m)O(n-1) (OCH(3))+ and V(m)O(n-1) (OH)(CH(3)OH)+, respectively.
通过电喷雾电离产生的裸钒氧化物和氢氧化物簇阳离子V(m)O(n)+和V(m)O(n - 1)(OH)+（m = 1 - 4，n = 1 - 10），使用质谱技术研究了它们与甲醇的反应活性。观察到了几种反应通道，如氢原子、甲基自由基或羟甲基自由基的提取、甲烷的消除以及加合物的形成。此外，发现甲醇脱氢生成甲醛通过四种不同途径发生。甲醛作为游离分子释放，要么是两个氢原子转移到簇上，要么是一个氧原子从簇转移到中性醇上并伴随水的消除。此外，甲醛在失去H2或中性水后附着在V(m)O(n)+上，分别生成阳离子V(m)O(n)(OCH(2))+或V(m)O(n - 1)(OCH(2))+。反应活性筛选表明，只有高价钒氧化物簇对H2吸收、氧转移和H2O消除具有反应活性，而较小的低价簇阳离子能够通过消除H2使甲醇脱氢。为了进行比较，还研究了甲醇与相应的氢氧化物簇离子V(m)O(n - 1)(OH)+的反应活性，其主要途径分别导致缩合产物和缔合产物的生成，即分别生成离子V(m)O(n - 1)(OCH(3))+和V(m)O(n - 1)(OH)(CH(3)OH)+。
