The elementary steps and active structures involved in thiophene hydrodesulfurization (HDS) are examined here through structural and functional assessments of Re and ReS_x catalysts prepared from ReO_x precursors by treatment in H₂ or H₂S. These samples retain their respective bulk phases at sulfur chemical potentials prevalent during HDS, because nucleation barriers inhibit the interconversion of isotropic Re metal and lamellar ReS_x layers. HDS turnover rates were much higher on ReS_x than Re, but both phases showed similar kinetic effects of thiophene, H₂, and H₂S and binding constants for adsorbed thiophene and S-atoms, consistent with a common mechanism involving active sites that differ in number but not in binding properties. In such elementary steps, the surface consists of a template of refractory S-atoms that are bound irreversibly, known to form even at H₂S/H₂ ratios much lower than in HDS practice. Interstices within such templates can reversibly bind reactive intermediates, thus allowing catalytic turnovers, and act as HDS active sites. The number of such interstices depends on MS bond strength, which is lower for particles with ReS_x than with Re bulk phases; their binding properties, however, are not dictated by the bulk phase, because they consist of those surface spaces that become capable of binding S-species weakly enough to allow their formation and removal as part of each catalytic turnover. On both Re and ReS_x, thiophene conversion rates are limited by the addition of one H-atom to bound thiophene to form intermediate species that give tetrahydrothiophene (THT) and C₄ hydrocarbons at a kinetic branch after this kinetically-relevant step. Thiophene pressures and H₂S/H₂ ratios do not influence THT/C₄ product ratios, which decrease as residence time increases because of secondary CS cleavage in THT to form C₄ products. Both products form in a single surface sojourn at similar site coverages by intermediates, as is also the case for secondary THT reactions. The effects of H₂ on these primary and secondary events indicate that the kinetic branching occurs at a bound intermediate with the H-content of dihydrothiophene, from which the CS bond cleavage transition state is also formed. As in CC and CO cleavage, CS bond scission requires H-removal from saturated reactants (THT) by (i) increasing the bond order of its surface attachment; (ii) weakening the CX bond being cleaved (X = C, O, S); and (iii) evolving H₂ to minimize entropy losses upon formation of the transition state.

此处，通过对在H ₂或H ₂ S中处理的，由ReO _x前驱体制备的Re和ReS _x催化剂的结构和功能评估，检查了涉及噻吩加氢脱硫（HDS）的基本步骤和活性结构。由于成核壁垒会抑制各向同性Re金属和层状ReS _x层的相互转化，因此在HDS期间普遍存在硫化学势。在ReS _x上，HDS转换率要比Re高得多，但是两个阶段都表现出相似的噻吩，H ₂和H ₂动力学效应。S和吸附的噻吩和S原子的结合常数，与涉及活性位点数量不同但结合特性不同的常见机制一致。在这样的基本步骤中，表面由不可逆结合的难熔S原子模板组成，已知它们甚至以比HDS实践中低得多的H ₂ S / H ₂比形成。此类模板中的空隙可以可逆地结合反应性中间体，从而实现催化转化，并充当HDS活性位点。此类空隙的数量取决于M S键的强度，对于具有ReS _x的颗粒而言较低相对于Re散装相而言；然而，它们的结合特性不是由本体相决定的，因为它们由那些能够弱结合S物种的表面空间组成，从而使得它们可以作为每个催化转化的一部分被形成和去除。在Re和ReS _x上，通过在该动力学相关步骤之后在动力学分支上添加一个H原子以键合噻吩以形成中间体，从而在动力学分支上生成四氢噻吩（THT）和C ₄烃，从而限制了噻吩的转化率。噻吩压力和H ₂ S / H ₂比率不影响THT / C ₄产物比率，其由于停留时间增加而降低，这是由于TH中二次C S裂解形成C_4个产品。两种产物都在一个单一的表面上形成中间体，在中间位置被相似的位置所覆盖，第二次THT反应也是如此。H ₂对这些主要事件和次要事件的影响表明，动力学支化发生在具有二氢噻吩H含量的结合中间体上，从该中间体也形成了C S键裂解过渡态。如在C C和C O裂解中一样，C S键断裂需要通过以下方法从饱和反应物（THT）中除去H：（i）增加其表面附着的键顺序；（ii）弱化被裂解的C X键（X = C，O，S）；（iii）使H ₂放出以在形成过渡态时使熵损失最小。