固体表面填隙H的诱导电矩对催化的重要贡献

Significant Contribution of the Induced Dipole of an Interstitial Hydrogen on Solid Surface to the Catalysis

我们在近期发表的工作中曾经指出,固体表面对填隙氢常施加泡利排斥作用,造成H原子性质的改变,增加其化学活性.简称为‘填隙H的泡利激活’.我们撰写此文目的是进一步定量地确认这一激活的真实性.着重说明,泡利激活产生填隙H的诱导电矩,它对催化起到关键作用.我们首先以简单双原子分子为例详细说明,形成分子共价键必须满足两个前提条件,即两原子密接时,必须满足‘基态能量趋同’和‘宇称匹配’(两个原子波固有的空间反演对称性相互适配)的要求.进而论证,泡利激活的表面填隙H充分满足这两个条件,原因是填隙H的诱导电矩对外来参与成键的原子(分子)的空间取向和能量具有显著的调制作用.经过严格论证,正是这种双重调制作用,使两个原子在碰撞时刻的基态能量必然趋同,同时达到宇称匹配.我们还强调,固体表面孔穴的尺寸必须和填隙H原子半径相匹配,才能保证泡利激活机制的成功运作.由此提供了对指定的化学反应如何选择催化剂的明确标准,这在应用中具有参考价值.我们将此泡利激活机制应用于一个实际而简单的化学反应,对以镍(Ni)为多相催化剂合成二氢化镁(MgH_(2))做出计算和定量分析.具体说明在这一反应中选择有效催化剂的办法.形象地演示了正是泡利激活填隙H电矩的双重调制作用促成了共价键Mg-H的形成,从而在理论上确认了泡利激活催化机制的合理性.最后提出一些预期的结论,期待得到实验的检验.

Recently we mentioned that the surface of solids often exerts Pauli repulsion on the interstitial hydrogen, which markedly changes the properties of atom H, and increases its chemical activity, which is simply called as ‘Pauli activation of interstitial H’. The purpose of this paper is further to quantitatively confirm the reality of this activation mechanism. We emphasize that, it is the H dipole induced by Pauli activation, which plays a key role for this catalysis. Taking a simple diatomic molecule as an example, we first explain in detail that two prerequisites have to be satisfied to form a molecular covalent bond, i.e., the requirements of both the ‘energy convergence’ of the ground states of two atoms and the ‘matching of parity’(the compatibility of intrinsic spatial reversal symmetry of two atomic waves) must be met when two atoms are in close contact. We further argue that the Pauli activated H on surface of solids just meets these preconditions due to the dual modulation effect of the induced H dipole on both the energy and the spatial orientation of the incoming foreign atom/molecule, participating in the bonding process with H, and inevitably facilitates the required convergence of the energies of ground states of two atoms as well as the matching of parity. We emphasize that the Pauli activation requires that the size of the pit/depression(hole) on the solids surface must match the radius of the interstitial H atom to ensure the effectiveness of Pauli activation. Accordingly it provides a clear criteria of selecting a suitable catalyst for the specific chemical reaction, which is valuable in practical applications. Taking a real and simple chemical reaction as an example, we make a calculation and quantitative discussion on the synthesis of MgH_(2), using Ni as the heterogeneous catalyst. Details of how to select a suitable catalyst are given. And how the dual modulation effect of the dipole of interstitial H facilitates the formation of the covalent bond Mg-H is clearly demonstrated. Therefore the rationality of the Pauli activation catalysis is confirmed theoretically. At end of this article, some predicted results are put forward, expected to be tested by future experiments.