Transition metal carbides have numerous applications and are known to excel in terms of hardness, thermal stability and conductivity. In particular, the Pt-like behavior of Mo and W carbides has...

To establish descriptors for the activity of Cu-Ga-based CO2-to-methanol hydrogenation catalysts, we prepared via co-grafting followed by a reduction in hydrogen, a series of materials containing 3-6 nm Cu1-xGax alloyed nanoparticles with variable xGa. They display a volcano-type activity behavior, where methanol formation is promoted for xGa < 0.13, while above poisoning effects are observed. In catalysts that are prepared via different methods and differ in the degree of Ga reduction, only the fraction of Ga0 in the formed Cu-Ga alloy matters for the catalytic activity. We were therefore able to establish that the concentration of Ga0 in the Cu-Ga alloyed precatalyst is the main descriptor of methanol formation activity.

Transition metal carbides have numerous applications and are known to excel in terms of hardness, thermal stability and conductivity. In particular, the Pt-like behavior of Mo and W carbides has led to a popularization of metal carbides in catalysis, ranging from electrochemically-driven reactions to thermal methane coupling. Herein, we show the dynamics of Mo and W carbides and the active participation of carbidic carbon in the formation of C2 products during methane coupling. A detailed mechanistic study reveals that the catalyst performance of these metal carbides can be traced back to its carbon diffusivity and exchange capability upon interaction with gas phase carbon (methane). A stable C2 selectivity over time on stream for Mo carbide (Mo2C) can be rationalized by fast carbon diffusion dynamics, while W carbide (WC) shows loss of selectivity due to slow diffusion leading to surface carbon depletion. This finding showcases that the bulk carbidic carbon of the catalyst plays a crucial role and that the metal carbide is not only responsible for methyl radical formation. Overall, this study supports the presence of a carbon equivalent to the Mars-Van Krevelen type mechanism for non-oxidative coupling of methane, thus introducing guiding principles to design and develop associated catalysts.

Non-oxidative coupling of methane (NOCM) is a sought-after reaction that has been studied for decades. Harsh reaction conditions (T >800°C) in the face of limited catalyst stability lead to rapid catalyst deactivation and strong coking, preventing application thus far. Recent reports have shown the significance of an interplay of catalyst nature and reaction conditions, whereas metal carbides have prevailed to play a crucial role which involves incorporation of carbidic carbon in C2Hx and aromatic products. This perspective gives an overview of proposed mechanistic pathways and considerations about experiment conditions in order to foster a rational catalyst design platform for NOCM.

A prototypical material for the oxidative coupling of methane (OCM) is Li/MgO, for which Li is known to be essential as a dopant to obtain high C2 selectivities. Herein, Li/MgO is demonstrated to be an effective catalyst for non‐oxidative coupling of methane (NOCM). Moreover, the presence of Li is shown to favor the formation of magnesium acetylide (MgC2), while pure MgO promotes coke formation as evidenced by solid‐state 13C NMR, thus indicating that Li promotes C–C bond formation. Metadynamic simulations of the carbon mobility in MgC2 and Li2C2 at the density functional theory (DFT) level show that carbon easily diffuses as a C2 unit at 1000°C. These insights suggest that the enhanced C2selectivity for Li‐doped MgO is related to the formation of Li and Mg acetylides