Dynamic Reorganization of Bimetallic Nanoparticles under Reaction Depending on the Support Nanoshape: The Case of RhPd over Ceria Nanocubes and Nanorods under Ethanol Steam Reforming

Nano-based biofuel production from low-cost lignocellulose biomass: environmental sustainability and economic approach

The use of nanomaterials in biofuel production from lignocellulosic biomass offers a promising approach to simultaneously address environmental sustainability and economic viability. This review provides an overview of the environmental and economic implications of integrating nanotechnology into biofuel production from low-cost lignocellulosic biomass. In this review, we highlight the potential benefits and challenges of nano-based biofuel production. Nanomaterials provide opportunities to improve feedstock pretreatment, enzymatic hydrolysis, fermentation, and catalysis, resulting in enhanced process efficiency, lower energy consumption, and reduced environmental impact. Conducting life cycle assessments is crucial for evaluating the overall environmental footprint of biofuel production. An economic perspective that focuses on the cost implications of utilizing nanomaterials in biofuel production is also discussed. A comprehensive understanding of both environmental and economic dimensions is essential to fully harness the potential of nanomaterials in biofuel production from lignocellulosic biomass and to move towards sustainable future energy.

Influence of the drying mode of support on the properties of Pd/Al2O3-ZrO2 materials used for methane combustion

This work constitutes a new trial to enhance the properties of palladium supported on alumina modified with zirconium used as catalysts for methane combustion. The effect of the support drying mode is studied. For this aim, Al2O3-ZrO2 binary oxides with zirconium loading of 2 and 5% in weight were prepared using sol-gel process then dried under ordinary or supercritical conditions. Palladium with a loading of 0.5% was deposited on the support by wet impregnation. Several techniques have been used to investigate differences between the two types of the derived catalysts.

Ultrastructure and Surface Composition of Glutathione-Terminated Ultrasmall Silver, Gold, Platinum, and Alloyed Silver-Platinum Nanoparticles (2 nm)

Alloyed ultrasmall silver-platinum nanoparticles (molar ratio Ag:Pt = 50:50) were prepared and compared to pure silver, platinum, and gold nanoparticles, all with a metallic core diameter of 2 nm. They were surface-stabilized by a layer of glutathione (GSH). A comprehensive characterization by high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), differential centrifugal sedimentation (DCS), and UV spectroscopy showed their size both in the dry and in the water-dispersed state (hydrodynamic diameter). Solution NMR spectroscopy (1H, 13C, COSY, HSQC, HMBC, and DOSY) showed the nature of the glutathione shell including the number of GSH ligands on each nanoparticle (about 200 with a molecular footprint of 0.063 nm2 each). It furthermore showed that there are at least two different positions for the GSH ligand on the gold nanoparticle surface. Platinum strongly reduced the resolution of the NMR spectra compared to silver and gold, also in the alloyed nanoparticles. X-ray photoelectron spectroscopy (XPS) showed that silver, platinum, and silver-platinum particles were at least partially oxidized to Ag(+I) and Pt(+II), whereas the gold nanoparticles showed no sign of oxidation. Platinum and gold nanoparticles were well crystalline but twinned (fcc lattice) despite the small particle size. Silver was crystalline in electron diffraction but not in X-ray diffraction. Alloyed silver-platinum nanoparticles were almost fully amorphous by both methods, indicating a considerable internal disorder.

Preformed Pt Nanoparticles Supported on Nanoshaped CeO2 for Total Propane Oxidation

Pt-based catalysts have been widely used for the removal of short-chain volatile organic compounds (VOCs), such as propane. In this study, we synthesized Pt nanoparticles with a size of ca. 2.4 nm and loaded them on various fine-shaped CeO2 with different facets to investigate the effect of CeO2 morphology on the complete oxidation of propane. The Pt/CeO2-o catalyst with {111} facets exhibited superior catalytic activity compared to the Pt/CeO2-r catalyst with {110} and {100} facets. Specifically, the turnover frequency (TOF) value of Pt/CeO2-o was 1.8 times higher than that of Pt/CeO2-r. Moreover, Pt/CeO2-o showed outstanding long-term stability during 50 h. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the excellent performance of Pt/CeO2-o is due to the prevalence of metallic Pt species, which promotes C-C bond cleavage and facilitates the rapid removal of surface formate species. In contrast, a stronger metal-support interaction in Pt/CeO2-r leads to easier oxidation of Pt species and the accumulation of intermediates, which is detrimental to the catalytic activity. Our work provides insight into the oxidation of propane on different nanoshaped Pt/CeO2 catalysts.

Shape-Controlled Pathways in the Hydrogen Production from Ethanol Steam Reforming over Ceria Nanoparticles

The ethanol surface reaction over CeO₂ nanooctahedra (NO) and nanocubes (NC), which mainly expose (111) and (100) surfaces, respectively, was studied by means of infrared spectroscopy (TPSR-IR), mass spectrometry (TPSR-MS), and density functional theory (DFT) calculations. TPSR-MS results show that the production of H₂ is 2.4 times higher on CeO₂-NC than on CeO₂-NO, which is rationalized starting from the different types of adsorbed ethoxy species controlled by the shape of the ceria particles. Over the CeO₂(111) surface, monodentate type I and II ethoxy species with the alkyl chain perpendicular or parallel to the surface, respectively, were identified. Meanwhile, on the CeO₂(100) surface, bidentate and monodentate type III ethoxy species on the checkerboard O-terminated surface and on a pyramid of the reconstructed (100) surface, respectively, are found. The more labile surface ethoxy species on each ceria nanoshape, which are the monodentate type I or III ethoxy on CeO₂-NO and CeO₂-NC, respectively, react on the surface to give acetate species that decompose to CO₂ and CH₄, while H₂ is formed via the recombination of hydroxyl species. In addition, the more stable monodentate type II and bidentate ethoxy species on CeO₂-NO and CeO₂-NC, respectively, give an ethylenedioxy intermediate, the binding of which is facet-dependent. On the (111) facet, the less strongly bound ethylenedioxy desorbs as ethylene, whereas on the (100) facet, the more strongly bound intermediate also produces CO₂ and H₂ via formate species. Thus, on the (100) facet, an additional pathway toward H₂ formation is found. ESR activity measurements show an enhanced H₂ production on the nanocubes.

Coke-resistant Ni-based bimetallic catalysts for the dry reforming of methane: effects of indium on the Ni/Al2O3 catalyst

In the quest for highly efficient coke-resistant catalysts for the dry reforming of methane (DRM) to produce syngas, a series of Ni–In/γ-Al2O3 catalysts with various Ni contents were prepared via a “two-solvent” method and used for the DRM reaction.

Simultaneous two-color X-ray absorption spectroscopy using Laue crystals at an inverse-compton scattering X-ray facility

X-ray absorption spectroscopy (XAS) is an element-selective technique that provides electronic and structural information of materials and reveals the essential mechanisms of the reactions involved. However, the technique is typically conducted at synchrotrons and usually only probes one element at a time. In this paper, a simultaneous two-color XAS setup at a laboratory-scale synchrotron facility is proposed based on inverse Compton scattering (ICS) at the Munich Compact Light Source (MuCLS), which is based on inverse Compton scattering (ICS). The setup utilizes two silicon crystals in a Laue geometry. A proof-of-principle experiment is presented where both silver (Ag) and palladium (Pd) K-edge X-ray absorption near-edge structure spectra were simultaneously measured. The simplicity of the setup facilitates its migration to other ICS facilities or maybe to other X-ray sources (e.g. a bending-magnet beamline). Such a setup has the potential to study reaction mechanisms and synergistic effects of chemical systems containing multiple elements of interest, such as a bimetallic catalyst system.

Ru-Ni bimetallic catalysts for steam reforming of xylene: effects of active metals and calcination temperature of the support

A series of Ru and Ni supported catalysts were prepared and their catalytic performance was evaluated in the steam reforming of xylenes. The effects of active metals, active metal loading sequence, and the calcination temperature of the support on the catalyst activity and stability were investigated. The bimetallic 2Ru → 15Ni catalyst shows much higher activity and stability than the monometallic 2Ru and 15Ni catalyst owing to the synergic effect of Ni and Ru. The 2Ru → 15Ni catalyst has the least coke deposition owing to its high conversion performance and much less coke precursor being formed on the catalyst surface. After decoking, most of the small-sized pores cannot be recovered because of the pore collapse under severe hydrothermal conditions. o-Xylene has the lowest reactivity due to electronic and steric effects. Besides the steam reforming reaction, demethylation and C–C cracking are also observed, forming benzene and toluene. The catalyst with a loading sequence of 15Ni → 2Ru shows high activity at low temperatures (550–600 °C), but undergoes an activity drop at high temperatures (625–650 °C) because the Ni sintering at high temperatures greatly affects the state of Ru on the catalyst. The catalyst with a loading sequence of 2Ru → 15Ni has an advantage at high temperatures owing to its better sintering resistance. The simultaneously loaded 2Ru ↔ 15Ni catalyst shows the lowest activity. The high calcination temperature of the support enhances the catalyst stability by eliminating the small-sized pores before reaction; on the other hand, the elimination of pores decreases the dispersion of the active metals. The 2Ru → 15Ni catalyst calcined at 1000 °C balances the active metal dispersion and resistance to sintering under severe hydrothermal conditions, showing the best activity and stability. The catalyst calcined at 1000 °C has the best coke resistance with only 0.166 g g_cat⁻¹ of coke formation after the 24 h durability test. The DTG results indicate that the carbon formed on the catalysts is mainly graphitic carbon.

The performance of the bimetallic 2Ru15Ni/La₂O₃–MgO–Al₂O₃ catalyst in the steam reforming of xylene greatly depends on the metal loading sequence and support calcination temperature.

A sinter-resistant catalytic system based on ultra-small Ni-Cu nanoparticles encapsulated in Ca-SiO2 for high-performance ethanol steam reforming

To enhance the catalytic performance of catalysts for the ethanol steam reforming (ESR) reaction, a facile reverse micelle strategy was adopted to prepare a core@shell Ni-Cu@Ca-SiO2 (Ni-Cu@CS) nanoreactor composed of an ultra-small Ni-Cu alloy (∼2.8 nm) encapsulated in Ca-functionalized SiO2 nanoparticles. Benefiting from its core@shell structural features and unique components, the Ni-Cu@CS nanoreactor exhibited superior activity (69.91% H2 selectivity and 99.99% ethanol conversion) and stability compared to reference samples. The regenerated Ni-Cu@CS nanoreactor showed high stability, maintaining 98.14% ethanol conversion and only 1.98 mg gcat-1 h-1 in carbon deposition. The high catalytic performance of Ni-Cu@CS is attributed to not only its encapsulated structure, which effectively prevented the sintering of neighboring Ni-Cu alloy nanoparticles, but also to its Ca-functionalized porous SiO2 shell, suppressing the carbon deposition. Moreover, its porous thin shell facilitated the mass transfer and diffusion of reactants and products. Thus, the Ni-Cu@CS nanoreactor is expected to become a new type of high-efficiency nanoreactor for the ESR reaction.

Ceria-Based Catalysts Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy: A Review

The development of better catalysts is a passionate topic at the forefront of modern science, where operando techniques are necessary to identify the nature of the active sites. The surface of a solid catalyst is dynamic and dependent on the reaction environment and, therefore, the catalytic active sites may only be formed under specific reaction conditions and may not be stable either in air or under high vacuum conditions. The identification of the active sites and the understanding of their behaviour are essential information towards a rational catalyst design. One of the most powerful operando techniques for the study of active sites is near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), which is particularly sensitive to the surface and sub-surface of solids. Here we review the use of NAP-XPS for the study of ceria-based catalysts, widely used in a large number of industrial processes due to their excellent oxygen storage capacity and well-established redox properties.

AP-XPS beamline, a platform for operando science at Pohang Accelerator Laboratory

Beamline 8A (BL 8A) is an undulator-based soft X-ray beamline at Pohang Accelerator Laboratory. This beamline is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), soft X-ray absorption spectroscopy (soft-XAS) and scanning photoemission microscopy (SPEM) experiments. BL 8A has two branches, 8A1 SPEM and 8A2 AP-XPS, that share a plane undulator, the first mirror (M1) and the monochromator. The photon beam is switched between the two branches by changing the refocusing mirrors after the monochromator. The acceptance angle of M1 is kept glancing at 1.2°, and Pt is coated onto the mirrors to achieve high reflectance, which ensures a wide photon energy range (100-2000 eV) with high resolution at a photon flux of ∼1013 photons s-1. In this article, the main properties and performance of the beamline are reported, together with selected experiments performed on the new beamline and experimental system.

Surface reconstruction of AgPd nanoalloy particles during the electrocatalytic formate oxidation reaction

Formate is a kind of carbon-neutral fuel that can be synthesized by electrochemical conversion of CO₂, however, the generated aqueous formate electrolyte is still short of potential application. Here, formate solution is proposed to be utilized as anode fuels of direct formate fuel cells through the formate oxidation reaction (FOR), and graphene supported AgPd nanoalloys (AgPd/rGO) are prepared to catalyze the FOR. Specifically, the mass activity of the as-prepared Ag₄₉Pd₅₁/rGO catalyst is 4.21 A mg^-1_Pd and the retention activity of Ag₄₉Pd₅₁/rGO is 49.1% of initial activity after successive 500 cycles, which is 2.48 and 3.03 times higher than that of unsupported Ag₅₁Pd₄₉ nanoalloys. When increasing the positive scan limit from 0.0 to 0.8 V, the mass activity of the Ag₄₉Pd₅₁/rGO catalyst increases from 2.32 to 6.03 A mg^-1_Pd and Pd surface coverage increases from 51.87% to 62.42%, indicating the occurrence of surface reconstruction where Pd atoms migrate to the surface of AgPd nanoalloys, and less intensive reconstruction is observed in unsupported Ag₅₁Pd₄₉ nanoalloys, whose mass activity increases from 1.35 to 2.49 A mg^-1_Pd. The driving force and kinetic path are calculated for the surface reconstruction induced by the adsorption of H, O and C atoms, in the case of C atoms on graphene, the segregation energy of surface Pd atoms in the AgPd nanoalloy is -1.16 eV, and the activation energy for the migration of subsurface Pd atoms to the surface is 0.54 eV, which are lower than the segregation (0.03 eV) and activation (2.06 eV) energy on a clean alloy surface.