Effective Inhibition of Ethane Generation on Fe₅C₂ Nanoparticles Doped with ppm Level of Pd for Selective Hydrogenation of Acetylene

Abstract

Overhydrogenation to ethane is most undesired in selective hydrogenation of acetylene. Monometallic Pd supported on common oxide supports such as alumina and silica suffers from susceptibility of ethane formation, and the ethylene selectivity is usually unsatisfactory. Herein, Fe5C2 was carefully synthesized and employed as a new kind support doped with a (5–600) ppm level of Pd for selective hydrogenation of acetylene. The catalyst with appropriate Pd loadings exhibited more efficient ethane suppression and much higher ethylene selectivity than the traditional α-Al2O3 supported Pd catalyst, with full acetylene conversion under 240 °C, and maintained good stability after a 200 h tolerance test. Characterization and DFT calculation results reveal that the excellent ethylene selectivity is mainly derived from the special interaction between Pd atoms and the Fe5C2 support. Hydrogenation of ethylene to ethane needs to cross extremely high activation energy barriers on the catalyst surface, and ethylene desorption more easily occurs on it. Doping the appropriate amount of Pd atoms on the Fe5C2 surface can increase the obstacle for polymerization and will cause the unsaturated C2 species to be more inclined to be hydrogenated into C2H4. This synergy effect also acts as a guide in alkane suppression for selective hydrogenation of other alkynes.

Mechanistic Understanding of Hydrocarbon Formation from CO2 Hydrogenation over χ-Fe5C2(111) and the Effect of H2O and Transition Metal Addition

“…Based on previous studies in the literature, − the introduction of other transition metals into χ-Fe 5 C 2 had unexpected effects on the catalytic performance, especially tuning the selectivity of products. For example, doping Pd into Fe 5 C 2 led to an enhanced selectivity to ethylene from acetylene hydrogenation . The theoretical study proved that doping transition metal Mn and Cr on the surfaces of Fe (100) and Fe 5 C 2 (100) promoted the dissociation of CO, whereas doping the surfaces by Ni and Cu was not conducive to the CO dissociation, leading to an altered product selectivity .…”

“…For example, doping Pd into Fe 5 C 2 led to an enhanced selectivity to ethylene from acetylene hydrogenation. 74 The theoretical study proved that doping transition metal Mn and Cr on the surfaces of Fe (100) and Fe 5 C 2 (100) promoted the dissociation of CO, whereas doping the surfaces by Ni and Cu was not conducive to the CO dissociation, leading to an altered product selectivity. 72 In addition, the FTS reaction was carried out on a series of Fe-M (M = Mn, Co, and Ni) spinel bimetallic iron catalysts.…”

Synthetic Strategies of Supported Pd-Based Bimetallic Catalysts for Selective Semi-Hydrogenation of Acetylene: A Review and Perspectives

“…In this context, the acetylene concentration is required to be removed to less than 5 ppm to meet the downstream production demand [ 1 , 4 , 5 , 8 ]. Acetylene impurities could be removed by several methods, among which the catalytically selective semi-hydrogenation to ethylene is the most widely used way in the industry due to its good economy, environmental friendliness, and convenience [ 5 , 6 , 9 ]. On the other hand, in academia, acetylene hydrogenation has also attracted much attention from researchers because it is usually selected to serve as a model reaction of selective hydrogenation to evaluate the performance and catalytic mechanism of catalysts [ 10 ].…”