Improving the Carbon Resistance of Ni-Based Steam Reforming Catalyst by Alloying with Rh: A Computational Study Coupled with Reforming Experiments and EXAFS Characterization

Abstract

Supported nickel catalysts are widely used in hydrocarbon steam reforming for producing hydrogen. Carbon deposition is a major cause of Ni catalyst deactivation. In this work, supported Ni and Ni/Rh catalysts were synthesized and tested for liquid hydrocarbon steam reforming. Carbon analysis on the spent catalysts illustrates that the carbon deposition is significantly reduced with inclusion of Rh. Extended X-ray Absorption Fine Structure (EXAFS) analysis indicates close interactions between Ni and Rh atoms. Density functional theory (DFT) results show that a Ni/Rh alloy is thermodynamically more stable than Ni and Rh alone at the synthesis and reaction temperatures. Adsorption, diffusion, and oxidation of carbon atoms over Ni and Ni/Rh alloy surfaces were examined by DFT calculations. Alloying with Rh reduces the stability of deposited carbon atoms and clusters over both terraces and steps of the catalyst. Moreover, Rh addition enhances the competition of oxidation reactions against carbon deposition by altering the relative diffusion rates and bond formation rates of the two processes.

Coprecipitation versus chemical vapour deposition to prepare Rh/Ni bimetallic catalysts

“…Consequently, enhanced activities were reported not only in conventional and commercial H 2 and syngas processes such as steam reforming [17,18], autothermal reforming [7,12,17,19,20] and oxyreforming [21][22][23][24], but also in more prone to carbon formation processes such as dry reforming [9,[25][26][27][28][29][30][31], ethanol reforming [32][33][34], biogas reforming [35] and, lastly, in fuel cell devices [17], in which large hydrocarbons were fed in systems operating under transient conditions [36,37]. Indeed, Rh promoted the gasification of adsorbed carbon by steam in the autothermal reforming of isooctane [38] and decreased carbon formation in the reforming of liquid hydrocarbons [39]. Moreover, Rh improved sulphur tolerance during steam reforming of methane [40] or S-containing liquid fuels [41].…”

Oxygen Atom Function: The Case of Methane Oxidation Mechanism to Synthesis Gas over a Pd Cluster

“…The coordination energies of the CH-Pd2 and CH-Pd2O systems were increased to −5.70 and −4.66 eV, respectively. These results indicated that the coordination energy decreased with the cracking process: CH4 < CH3 < CH2 < CH < C [26,37,38]. They also revealed that the interaction between CHx (x = 0-4) and the catalyst was reduced by the introduction of the oxygen atom.…”

“…As shown in Figure 2 and Table 1, CH 4 dissociation catalyzed by Pd 2 and Pd 2 O results in an exothermic formation of CH 4 -Pd 2 and CH 4 -Pd 2 O systems. In the CH 4 -Pd 2 system, the length of the C-Pd bond was 2.657 Å, while the length decreased to 2.432 Å in CH 4 -Pd 2 O [37]. The coordination energy of the two systems was -0.34 and -0.87 eV, respectively.…”

“…With similar reaction paths, methane dehydrogenation processes are presented as four competitive reaction steps [36][37][38][39]: methyl (CH 3 ), methylene (CH 2 ), methylidene (CH), and carbon (C) were generated in an orderly fashion during the cracking. The stable configurations of CH 4 -Pd 2 (o), CH 3 -Pd 2 (o), CH 2 -Pd 2 (o), and CH-Pd 2 (o) were obtained by geometry optimization, respectively.…”

In Situ and Surface-Enhanced Raman Spectroscopy Study of Electrode Materials in Solid Oxide Fuel Cells

“…For example, decorating La 1-x Sr x Co 1-y Fe y O 3-δ (LSCF) porous electrodes with certain nanoparticles such as Sm 1-x Sr x CoO 3-δ (SSC) and Ce 1-x Sm x O 2-δ (SDC) has been reported to reduce polarization resistances [26,27], whereas coating LSCF surfaces with La 1-x Sr x MnO 3-δ (LSM) can improve long-term stabilities [28]. Carbon deposition on nickel-based anodes can also be alleviated through modifications such as BaO, BZCYYb, or BZY, which are catalysts that can facilitate the gasification of deposited carbon atoms [3,9,29,30].…”