First-Principles Study of Structure Sensitivity of Ethylene Glycol Conversion on Platinum

Abundant Exterior/Interior Active Sites Enable Three-Dimensional PdPtBiTe Dumbbells C-C Cleavage Electrocatalysts for Actual Alcohol Fuel Cells

Developing high-activity electrocatalysts is of great significance for the commercialization of direct alcohol fuel cells (DAFCs), but it still faces challenges. Herein, three-dimensional (3D) porous PdPtBiTe dumbbells (DBs) were successfully fabricated via the visible photoassisted method. The alloying effect, defect-rich surface/interface and nanoscale cavity, and open pores make the 3D PdPtBiTe DBs a comprehensive and remarkable electrocatalyst for the C1-C3 alcohol (ethanol, ethylene glycol, glycerol, and methanol) oxidation reaction (EOR, EGOR, GOR, and MOR, respectively) in an alkaline electrolyte, and the results of in situ Fourier transform infrared spectra revealed a superior C-C bond cleavage ability. The 3D PdPtBiTe DBs exhibit ultrahigh EOR, EGOR, GOR, and MOR mass activities of 25.4, 23.2, 16.8, and 18.3 A mgPd + Pt-1, respectively, considerably surpassing those of the commercial Pt/C and Pd/C. Moreover, the mass peak power densities of 3D PdPtBiTe DBs in actual ethanol, ethylene glycol, glycerol, or methanol fuel cells increase to 409.5, 501.5, 558.0, or 601.3 mW mgPd + Pt-1 in O2, respectively. This study provides a new class of multimetallic nanomaterials as state-of-the-art multifunctional anode electrocatalysts for actual DAFCs.

Selective Ethylene Glycol Oxidation to Formate on Nickel Selenide with Simultaneous Evolution of Hydrogen

There is an urgent need for cost-effective strategies to produce hydrogen from renewable net-zero carbon sources using renewable energies. In this context, the electrochemical hydrogen evolution reaction can be boosted by replacing the oxygen evolution reaction with the oxidation of small organic molecules, such as ethylene glycol (EG). EG is a particularly interesting organic liquid with two hydroxyl groups that can be transformed into a variety of C1 and C2 chemicals, depending on the catalyst and reaction conditions. Here, a catalyst is demonstrated for the selective EG oxidation reaction (EGOR) to formate on nickel selenide. The catalyst nanoparticle (NP) morphology and crystallographic phase are tuned to maximize its performance. The optimized NiS electrocatalyst requires just 1.395 V to drive a current density of 50 mA cm^-2 in 1 m potassium hydroxide (KOH) and 1 m EG. A combination of in situ electrochemical infrared absorption spectroscopy (IRAS) to monitor the electrocatalytic process and ex situ analysis of the electrolyte composition shows the main EGOR product is formate, with a Faradaic efficiency above 80%. Additionally, C2 chemicals such as glycolate and oxalate are detected and quantified as minor products. Density functional theory (DFT) calculations of the reaction process show the glycol-to-oxalate pathway to be favored via the glycolate formation, where the CC bond is broken and further electro-oxidized to formate.

Influence of different microstructures of cobalt on the catalytic activity for amination of ethylene glycol: comparison of HCP cobalt and FCC cobalt

The fcc-Co catalyst shows high catalytic activity for the synthesis of primary amines by ethylene glycol amination, which is superior to that of the hcp-Co catalyst.

Effect of Potassium for Propylene Epoxidation on Cu2O(111) by Molecular Oxygen: A DFT Study

In the present work, spin-polarized density functional theory (DFT) calculations with a Hubbard U correction were employed to investigate the effect of potassium for propylene epoxidation on Cu2O(111) surface by...

Selective valorization of lignin to phenol by direct transformation of Csp2-Csp3 and C-O bonds

Phenol is an important commodity chemical in the industry, which is currently produced using fossil feedstocks. Here, we report a strategy to produce phenol from lignin by directly deconstructing C_sp2-C_sp3 and C-O bonds under mild conditions. It was found that zeolite catalyst could efficiently catalyze both the direct C_sp2-C_sp3 bond breakage to remove propyl structure and aliphatic β carbon-oxygen (C_β-O) bond hydrolysis to form OH group on the aromatic ring. The yield of phenol could reach 10.9 weight % with a selectivity of 91.8%. In this unique route, water was the only reactant besides lignin. A scale-up experiment showed that 4.1 g of pure phenol could be obtained from 50.0 g of lignin. The reaction pathway was proposed by a combination of control experiments and density functional theory studies. This work opens the way for producing phenol from lignin by direct transformation of C_sp2-C_sp3 and C-O bonds in lignin.

Ab initio investigation of the role of transition-metal dopants in the adsorption properties of ethylene glycol on doped Pt(100) surfaces

Ethylene glycol (EG) has been considered as a promising alcohol for direct alcohol fuel cells, however, our atomistic understanding of its interaction with doped transition-metal (TM) substrates is not well established. Here, we employed density functional theory calculations within the additive van der Waals D3 correction to improve our atomistic understanding of the role of TM dopants on the adsorption properties of EG on undoped and doped Pt(100) surfaces, namely, Pt₈TM₁/Pt₉/Pt(100) and Pt₉/Pt₈TM₁/Pt(100), where substitutional TM dopants (Fe, Co, Ni, Ru, Rh and Pd) are located within the topmost or subsurface Pt(100) layers, respectively. Except for Pd, all the studied TM dopants showed strong energetic preference for the subsurface layer, which can be explained by the segregation energy and charge effects, and it is not affected by the EG adsorption. In the lowest energy configurations of the undoped and doped substrates, EG binds via one OH group, with the anionic O atom located close to the on-top cationic TM site and the H atom parallel to the surface and pointing towards the bridge site. However, at slightly higher energy configurations, EG adsorbs via one OH with the C-C bond almost perpendicular to the surface, or via both OH groups. As expected, the adsorption is stronger on Pt₈TM₁/Pt₉/Pt(100) with EG (OH group) bound to the cationic TM site and a O-TM distance of about 2 Å. Furthermore, doping enhanced the adsorption energy, and hence, decreased the distance between EG and the surface. For all substrates, adsorption induces a reduction of the work function, which is larger for the adsorption of EG via two OH groups.

Selective Oxidation of Propylene on Cu2O(111) and Cu2O(110) Surfaces: A Systematically DFT Study

Density functional theory calculations with a Hubbard U correction were used to investigate the selective oxidation of propylene on Cu₂O(111) and Cu₂O(110) surfaces, and the mechanism for the selective oxidation of propylene was discussed. On both surfaces, acrolein can be generated by two H-stripping reactions in the allylic hydrogen stripping path, while propylene oxide (PO), propanal, and acetone can be created through the propylene oxametallacycle intermediates in the epoxidation path. Our calculation results indicated that Cu₂O has a high crystal plane-controlled phenomenon for the selective oxidation of propylene. It was found that the formations of propanal and acetone are unfavorable kinetically and acrolein is the main product on the (111) surface. On the (110) surface, the activation barrier of acrolein formation is too high to produce and PO becomes the favored product, which is different from the case of the (111) surface. Moreover, energetic span model analysis was carried out to discuss the selective oxidation of propylene on these two surfaces and confirm the above calculations. The present study can help people to design the proper crystal plane catalyst to get the target product of PO with high selectivity and activity in the selective oxidation of propylene.

Recent advances in the electrooxidation of biomass-based organic molecules for energy, chemicals and hydrogen production

The recent developments in biomass-derivative fuelled electrochemical converters for electricity or hydrogen production together with chemical electrosynthesis have been reviewed.

The polyol process: a unique method for easy access to metal nanoparticles with tailored sizes, shapes and compositions

After about three decades of development, the polyol process is now widely recognized and practised as a unique soft chemical method for the preparation of a large variety of nanoparticles which can be used in important technological fields. It offers many advantages: low cost, ease of use and, very importantly, already proven scalability for industrial applications. Among the different classes of inorganic nanoparticles which can be prepared in liquid polyols, metals were the first reported. This review aims to give a comprehensive account of the strategies used to prepare monometallic nanoparticles and multimetallic materials with tailored size and shape. As regards monometallic materials, while the preparation of noble as well as ferromagnetic metals is now clearly established, the scope of the polyol process has been extended to the preparation of more electropositive metals, such as post-transition metals and semi-metals. The potential of this method is also clearly displayed for the preparation of alloys, intermetallics and core-shell nanostructures with a very large diversity of compositions and architectures.

Geometrical flexibility of platinum nanoclusters: impacts on catalytic decomposition of ethylene glycol

Catalytic decomposition of ethylene glycol on the Pt₁₃ cluster was studied as a model system for hydrogen production from a lignocellulosic material. Ethylene glycol was chosen as a starting material because of two reasons, it is the smallest oxygenate with a 1 : 1 carbon to oxygen ratio and it contains the C-H, O-H, C-C, and C-O bonds also present in biomass. Density functional theory calculations were employed for predictions of reaction pathways for C-H, O-H, C-C and C-O cleavages, and Brønsted-Evans-Polanyi relationships were established between the final state and the transition state for all mechanisms. The results show that Pt₁₃ catalyzes the cleavage reactions of ethylene glycol more favourably than a Pt surface. The flexibility of Pt₁₃ clusters during the reactions is the key factor in reducing the activation barrier. Overall, the results demonstrate that ethylene glycol and thus biomass can be efficiently converted into hydrogen using platinum nanoclusters as catalysts.

Differentiation of the C–O and C–C bond scission mechanisms of 1-hexadecanol on Pt(111) and Ru(0001): a first principles analysis

The major product on Pt(111) is hexadecane, whereas it is pentadecane on Ru(0001).

The effect of potassium on steam-methane reforming on the Ni4/Al2O3 surface: a DFT study

Steam-methane reforming is a method of converting natural gas to syngas, and the additive K could affect the activity of steam-methane reforming on Ni catalyst supported by Al₂O₃.

First-principles study of single transition metal atoms on ZnO for the water gas shift reaction

A single Ni atom substituted on a ZnO surface is a promising catalyst for the water gas shift reaction.

Theoretical Heterogeneous Catalysis: Scaling Relationships and Computational Catalyst Design

Scaling relationships are theoretical constructs that relate the binding energies of a wide variety of catalytic intermediates across a range of catalyst surfaces. Such relationships are ultimately derived from bond order conservation principles that were first introduced several decades ago. Through the growing power of computational surface science and catalysis, these concepts and their applications have recently begun to have a major impact in studies of catalytic reactivity and heterogeneous catalyst design. In this review, the detailed theory behind scaling relationships is discussed, and the existence of these relationships for catalytic materials ranging from pure metal to oxide surfaces, for numerous classes of molecules, and for a variety of catalytic surface structures is described. The use of the relationships to understand and elucidate reactivity trends across wide classes of catalytic surfaces and, in some cases, to predict optimal catalysts for certain chemical reactions, is explored. Finally, the observation that, in spite of the tremendous power of scaling relationships, their very existence places limits on the maximum rates that may be obtained for the catalyst classes in question is discussed, and promising strategies are explored to overcome these limitations to usher in a new era of theory-driven catalyst design.

1,2-Ethanediol and 1,3-Propanediol Conversions over (MO3)3 (M = Mo, W) Nanoclusters: A Computational Study

The dehydration and dehydrogenation reactions of one and two 1,2-ethanediol and 1,3-propanediol molecules on (MO3)3 (M = Mo, W) nanoclusters have been studied computationally using density functional and coupled cluster (CCSD(T)) theory. The reactions are initiated by the formation of a Lewis acid-base complex with an additional hydrogen bond. Dehydration is the dominant reaction proceeding via a metal bisdiolate. Acetaldehyde, the major product for 1,2-ethanediol, is produced by α-hydrogen transfer from one CH2 group to the other. For 1,3-propanediol, the C-C bond breaking pathways to produce C2H4 and HCH═O simultaneously and proton transfer to generate propylene oxide have comparable barrier energies. The barrier to produce propanal from the propylene oxide complex is less than that for epoxide release from the cluster. On the Mo3O9 cluster, a redox reaction channel for 1,2-ethanediol to break the C-C bond to form two formaldehyde molecules and then to produce C2H4 is slightly more favorable than the formation of acetaldehyde. For W(VI), the energy barrier for the reduction pathway is larger due to the lower reducibility of W3O9. Similar reduction on Mo(VI) for 1,3-propanediol to form propene is not a favorable pathway compared with the other pathways as additional C-H bond breaking is required in addition to breaking a C-C bond. The dehydrogenation and dehydration activation energies for the selected glycols are larger than the reactions of ethanol and 1-propanol on the same clusters. The CCSD(T) method is required because density functional theory with the M06 and B3LYP functionals does not predict quantitative energies on the potential energy surface. The M06 functional performs better than does the B3LYP functional.

Aqueous phase reforming and hydrodeoxygenation of ethylene glycol on Pt/SiO2–Al2O3: effects of surface acidity on product distribution

Aqueous-phase reforming and hydrodeoxygenation of ethylene glycol were investigated on Pt/SiO₂–Al₂O₃. The Pt/SiO₂–Al₂O₃ with Si/Al ratio of 0.1 showed a higher activity due to an abundant acidic sites with small platinum crystallites and a lower coke deposition.

Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111)

Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3-4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.