Surface restructuring of Cu-based single-atom alloy catalysts under reaction conditions: the essential role of adsorbates

Abstract

The stabilities and catalytic performances of single-atom alloy (SAA) structures under the reaction conditions of acetylene hydrogenation are thoroughly examined utilizing density functional theory (DFT) calculations. Four Cu-based alloys with stable SAA structures reported before, namely PdCu, PtCu, RhCu and NiCu alloys, are investigated here. We find that the SAA structures of PdCu and PtCu are stable during the reaction, whilst the RhCu-SAA and NiCu-SAA structures are thermodynamically unstable upon acetylene adsorption and surface restructuring through the aggregation of the Rh and Ni atoms on the surfaces may also happen. It is also found that all the investigated structures of RhCu and NiCu alloys may give rise to the further hydrogenation of ethylene. However, desorption of ethylene is favored over the PdCu-SAA and PtCu-SAA surfaces, indicating that acetylene could be selectively hydrogenated to ethylene over these two surfaces, which is consistent with the experimental observations reported in the literature. Our work provides new understandings regarding SAA surface structures under reaction conditions and their catalytic reaction performances upon aggregation of the doped metal atoms.

CO-Induced Aggregation and Segregation of Highly Dilute Alloys: A Density Functional Theory Study

“…C2H2) or chelating. 72 In addition to the weak interactions between dopant atoms of the (100) 2NN dimer, we find that CO-CO interactions are also small as a result of the large distance between the dopant atoms. This is reflected by the relaxed geometry of the two CO molecules, which remain sharply vertical to the dopant top sites (see bottom inset in the legend of Figure 8(c)).…”

“…It should be noted that the same shift regarding the preference for aggregate formation has been observed upon C2H2 adsorption on Ni/Cu(111). 72 We find that the type of the most stable adsorption site is crucial to the stability of the aggregate phase versus the SAA phase. In particular, the formation of (100) 1NN…”

Lonely Atoms with Special Gifts: Breaking Linear Scaling Relationships in Heterogeneous Catalysis with Single-Atom Alloys

“…Though the results of the DFT calculations depend on the exchange-correlation functional used, and quantitatively one should not put too much weight on the precise numbers obtained, DFT (with standard generalized-gradient approximation functionals) has proven to be very useful in understanding trends in heterogeneous catalysis and indeed in rationalizing experimental catalytic performance of SAAs. [72][73][84][85][86][87][88][89] DFT has also been used to explain how SAAs can exhibit combined low temperature C-H activation and coke resistance 65 (see section 3), to justify why SAAs have excellent tolerance to poisoning by CO, 90 to aid in SAA surface characterization, 75 and to rationalize their ability to perform dry, nonoxidative dehydrogenation of alcohols. 79 Most recently, simulation using DFT has become more exploratory.…”

Carbon Monoxide Poisoning Resistance and Structural Stability of Single Atom Alloys

“…Additionally, we recognize that the presence of adsorbates may induce structural changes in binary alloy materials, such as segregation of atoms from the bulk into the surface layer, as well as promoting aggregation and island formation [26][27][28][29][30][31][32][33][34]. Such changes are caused by differences in adsorption behaviour between an adsorbate on each metallic component of the alloy; these differences can offset or increase the energy change upon restructuring of the material.…”