Pt catalysts modified with Bi: Enhancement of the catalytic activity for alcohol oxidation in alkaline media

Recent Advances on Electro-Oxidation of Ethanol on Pt- and Pd-Based Catalysts: From Reaction Mechanisms to Catalytic Materials

“…Adsorbed CO, C1 and C2 hydrocarbon residues have been identified as the major adsorbed intermediates on Pt-or Pd-based catalysts, while acetaldehyde and acetic acid have been detected as the main by-products using techniques such as infrared spectroscopy [13][14][15][16][17][18][19][20][21][22][23][24][25][26], online DEMS [27][28][29][30][31][32][33][34][35][36][37], ion chromatography [56,57], and liquid chromatography [14]. However, EOR has been shown to occur via a series of complex reactions involving a number of sequential and parallel reaction steps, thus resulting in more than 40 possible volatile and adsorbed intermediates or oxidative derivatives [43].…”

“…To address these two issues, many efforts have been made to combine traditional electrochemical methods (cyclic voltammetry, chronoamperometry, rotating disc electrodes, etc.) with other physicochemical methods, such as in situ FTIR [9,[13][14][15][16][17][18][19][20][21][22][23][24], broadband sum-frequency generation (BB-SFG) spectroscopy [58], DEMS [16,[27][28][29][30][31][32][33][34][35][36], HPLC [56,57], GC [14], electrochemical quartz crystal microbalance (EQCM) [59] and in situ NMR [60] to probe the adsorbed intermediates and/or quantify the reaction products and by-products [56]. We devote the following section to summarize and discuss how these techniques were used for product quantification as well as the clarification of intermediates, starting with FTIR studies and followed by mass spectrometric results.…”

“…In fact, mass spectrometry has often been used to study EOR in conjunction with IR spectroscopy. Studies using DEMS [28][29][30][31][32][33][34][35][36][37], electrochemical thermal desorption mass spectroscopy (ECTDMS) [71], and multipurpose electrochemical mass spectrometry studies (MPEMS) [29] have drawn the conclusion that all mono-or bi-aliphatic alcohols, except tertiary ones, yield minor amounts of CO2 with the corresponding aldehydes or keto-compounds as major products during their electro-oxidation. Typically, on-line DEMS, especially under well-defined transport and diffusion conditions, has the ability to quantitatively determine kinetic parameters (reaction orders, activation energies, steady-state rates) for the overall EOR, and also for the partial reactions leading to the individual reaction products such as CO2, acetic acid, and acetaldehyde [16,[30][31][32][33]35,72].…”

“…Regardless of the media, Pt-based materials represent the benchmark catalysts for ethanol oxidation. Elements such as Ru [32,33,35,60,82,83], Sn [15,32,33,35,80,[84][85][86], Pb [21,[87][88][89][90][91], Bi [36,89,90,92,93], Re [86], Sb [93], Ir [94], Au [95], Ce [96], Rh [81,97], Pd [81,98,99], Fe [100], Ni [95,101], P [102], Mo [83,103] have been widely employed to enhance the activity and selectivity. In addition, metal oxides, such as MgO, CeO2, ZrO2, SnOx [76,94,104] RuO2, PbOx [88] have also been investigated for facilitating the removal of CO.…”

“…A detailed understanding of the reaction mechanism and in particular of the rate-limiting step(s) in EOR under continuous reaction conditions is of critical importance for the design of highly active catalysts [11,12]. Although numerous experimental studies using Fourier transform infrared spectroscopy (FTIR) [13][14][15][16][17][18][19][20][21][22][23][24][25][26] or differential electrochemical mass spectrometry (DEMS) [27][28][29][30][31][32][33][34][35][36][37], as well as theoretical studies [38][39][40][41][42][43][44][45] have been conducted to understand the EOR process, a detailed mechanism of EOR remains unclear or even contradictory. Nevertheless, a so-called dual-pathway (C1 and C2) mechanism has been largely agreed upon: the C1 pathway proceeds via adsorbed carbon monoxide (COads) intermediate to form CO2 (or carbonate in alkaline solutions) by delivering 12 electrons, and the C2 pathway mainly leads to the formation of acetic acid (or acetate in alkaline solutions) by delivering four electrons and/or acetaldehyde by delivering two electrons.…”