Methane Activation on Bimetallic Catalysts: Properties and Functions of Surface Ni−Ag Alloy

Recent Advances in Bimetallic Catalysts for Methane Steam Reforming in Hydrogen Production: Current Trends, Challenges, and Future Prospects

As energy demand continues to rise and the global population steadily grows, there is a growing interest in exploring alternative, clean, and renewable energy sources. The search for alternatives, such as green hydrogen, as both a fuel and an industrial feedstock, is intensifying. Methane steam reforming (MSR) has long been considered a primary method for hydrogen production, despite its numerous advantages, the activity and stability of the conventional Ni catalysts are major concerns due to carbon formation and metal sintering at high temperatures, posing significant drawbacks to the process. In recent years, significant attention has been given to bimetallic catalysts as a potential solution to overcome the challenges associated with methane steam reforming. Thus, this review focuses on the recent advancements in bimetallic catalysts for hydrogen production through methane steam reforming. The review explores various aspects including reactor type, catalyst selection, and the impact of different operating parameters such as reaction temperature, pressure, feed composition, reactor configuration, and feed and sweep gas flow rates. The analysis and discussion revolve around key performance indicators such as methane conversion, hydrogen recovery, and hydrogen yield.

Single atom alloys vs. phase separated alloys in Cu, Ag, and Au atoms with Ni(111) and Ni, Pd, and Pt atoms with Cu(111): a theoretical exploration

A single-atom alloy (SAA) consisting of an abundant metal host and a precious metal guest is a promising catalyst to reduce the cost without a loss of activity. DFT calculations of Ni- and Cu-based alloys nX/M(111) (X = Cu, Ag, or Au for M = Ni; X = Ni, Pd, or Pt for M = Cu; n = 1-4) reveal that a phase-separated alloy (PSA) is produced by Cu atoms with Ni(111) but an SAA is produced by Au atoms with Ni(111) and Pd and Pt atoms with Cu(111). In the Ni(111)-based Ag alloy and Cu(111)-based Ni alloy, the relative stabilities of the SAA and PSA depend on coverages of Ag on Ni(111) and Ni on Cu(111). The interaction energy (E_int) between the X_n cluster and M(111) host is larger than that between one X atom and the M(111) host, because the X_n cluster forms more bonding interactions with the M(111) host than does one X atom. When going from one X atom to the X₄ cluster, the E_int values of Au and Pt clusters respectively with Ni(111) and Cu(111) increase to a lesser extent than those of Cu and Ni clusters respectively with Ni(111) and Cu(111). Consequently, Au and Pt atoms tend to form SAAs respectively with Ni(111) and Cu(111) hosts compared to Cu and Ni atoms. This trend in the E_int value is determined by the valence orbital energies of the X atom and the X_n cluster. Cu atoms in nCu/Ni(111) have a slightly positive charge but Ag atoms in nAg/Ni(111), Au atoms in nAu/Ni(111), and Ni, Pd, and Pt atoms in nX/Cu(111) (X = Ni, Pd, or Pt) have a negative charge. The negative charge increases in the order Ag < Au in nX/Ni(111) and Ni < Pd < Pt in nX/Cu(111). The Fermi level decreases in energy in the order nCu/Ni(111) ≥ Ni(111) > nAg/Ni(111) > nAu/Ni(111) and Cu(111) ≥ nNi/Cu(111) > nPd/Cu(111) > nPt/Cu(111). The d valence band center decreases in energy in almost the same order. The CO adsorption energy decreases in the order Ni(111) ∼ nCu/Ni(111) > nAg/Ni(111) ∼ nAu/Ni(111) and Cu(111) > nNi/Cu(111) > nPd/Cu(111) > nPt/Cu(111). These properties are explained based on the electronic structures.

Effects of alloying for steam or dry reforming of methane: a review of recent studies

A survey on the catalytic nature of Ni-based alloy catalysts in recent years provides a direction for future catalyst development.