The Nature of Loading-Dependent Reaction Barriers over Mixed RuO2/TiO2 Catalysts

Selective Adsorption of Chlorine Species on RuO2 Sites for Efficient Elimination of Vinyl Chloride on the Ru/SnO2 Catalyst

The main bottleneck in the catalytic combustion of chlorinated volatile organic compounds (CVOCs) is deactivation and the production of chlorine-containing byproducts originating from the chlorine species deposited on the catalyst. Herein, Ru supported on SnO2 (Ru/SnO2) was prepared with the lattice matching principle. As RuO2 and SnO2 are both rutile phases, Ru species were present as highly dispersed RuO2 particles on the Ru/SnO2 catalyst. These particles adsorbed chlorine species with greater efficiency during the CVOCs combustion, thereby protecting the oxygen vacancies. Therefore, the double sites, oxygen vacancy to oxidize and RuO2 to adsorb chlorine species, on the Ru/SnO2 catalyst led to a notable enhancement in activity, stability, and byproduct selectivity. In contrast, the high dispersion of Ru species on the CeO2 support, as the typical catalyst for chlorinated hydrocarbon combustion, gave rise to a predominantly Ru-O-Ce structure. This structure did not prevent the adsorption of chlorine species on the oxygen vacancies, resulting in deactivation at low temperatures and an increased polychlorinated byproduct concentration. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) further corroborated the variation in the adsorption sites of chlorine species on the two catalysts. This work provides a new strategy for designing efficient Ru-based catalysts for catalytic CVOCs combustion.

Defective TiOx overlayers catalyze propane dehydrogenation promoted by base metals

The industrial catalysts utilized for propane dehydrogenation (PDH) to propylene, an important alternative to petroleum-based cracking processes, either use expensive metals or metal oxides that are environmentally unbenign. We report that a typically less-active oxide, titanium oxide (TiO2), can be combined with earth-abundant metallic nickel (Ni) to form an unconventional Ni@TiOx catalyst for efficient PDH. The catalyst demonstrates a 94% propylene selectivity at 40% propane conversion and superior stability under industrially relevant conditions. Complete encapsulation of Ni nanoparticles was allowed at elevated temperatures (>550°C). A mechanistic study suggested that the defective TiOx overlayer consisting of tetracoordinated Ti sites with oxygen vacancies is catalytically active. Subsurface metallic Ni acts as an electronic promoter to accelerate carbon-hydrogen bond activation and hydrogen (H2) desorption on the TiOx overlayer.

Confinement-Induced Indium Oxide Nanolayers Formed on Oxide Support for Enhanced CO2 Hydrogenation Reaction

An enclosed nanospace often shows a significant confinement effect on chemistry within its inner cavity, while whether an open space can have this effect remains elusive. Here, we show that the open surface of TiO2 creates a confined environment for In2O3 which drives spontaneous transformation of free In2O3 nanoparticles in physical contact with TiO2 nanoparticles into In oxide (InOx) nanolayers covering onto the TiO2 surface during CO2 hydrogenation to CO. The formed InOx nanolayers are easy to create surface oxygen vacancies but are against over-reduction to metallic In in the H2-rich atmospheres, which thus show significantly enhanced activity and stability in comparison with the pure In2O3 catalyst. The formation of interfacial In-O-Ti bonding is identified to drive the In2O3 dispersion and stabilize the metastable InOx layers. The InOx overlayers with distinct chemistry from their free counterpart can be confined on various oxide surfaces, demonstrating the important confinement effect at oxide/oxide interfaces.

Significance of Epitaxial Growth of PtO2 on Rutile TiO2 for Pt/TiO2 Catalysts

TiO2-supported Pt species have been widely applied in numerous critical reactions involving photo-, thermo-, and electrochemical-catalysis for decades. Manipulation of the state of the Pt species in Pt/TiO2 catalysts is crucial for fine-tuning their catalytic performance. Here, we report an interesting discovery showing the epitaxial growth of PtO2 atomic layers on rutile TiO2, potentially allowing control of the states of active Pt species in Pt/TiO2 catalysts. The presence of PtO2 atomic layers could modulate the geometric configuration and electronic state of the Pt species under reduction conditions, resulting in a spread of the particle shape and obtaining a Pt/PtO2/TiO2 structure with more positive valence of Pt species. As a result, such a catalyst exhibits exceptional electrocatalytic activity and stability toward hydrogen evolution reaction, while also promoting the thermocatalytic CO oxidation, surpassing the performance of the Pt/TiO2 catalyst with no epitaxial structure. This novel epitaxial growth of the PtO2 structure on rutile TiO2 in Pt/TiO2 catalysts shows its potential in the rational design of highly active and economical catalysts toward diverse catalytic reactions.

Electroreductive coupling of benzaldehyde by balancing the formation and dimerization of the ketyl intermediate

Electroreductive coupling of biomass-derived benzaldehyde offers a sustainable approach to producing value-added hydrobenzoin. The low efficiency of the reaction mainly ascribes to the mismatch of initial formation and subsequent dimerization of ketyl intermediates (Ph-CH = O → Ph-C·-OH → Ph-C(OH)-C(OH)-Ph). This paper describes a strategy to balance the active sites for the generation and dimerization of ketyl intermediates by constructing bimetallic Pd/Cu electrocatalysts with tunable surface coverage of Pd. A Faradaic efficiency of 63.2% and a hydrobenzoin production rate of up to 1.27 mmol mg-1 h-1 (0.43 mmol cm-2 h-1) are achieved at -0.40 V vs. reversible hydrogen electrode. Experimental results and theoretical calculations reveal that Pd promotes the generation of the ketyl intermediate, and Cu enhances their dimerization. Moreover, the balance between these two sites facilitates the coupling of benzaldehyde towards hydrobenzoin. This work offers a rational strategy to design efficient electrocatalysts for complex reactions through the optimization of specified active sites for different reaction steps.

Titanium nitride as a promising sodium-ion battery anode: interface-confined preparation and electrochemical investigation

The search for new electrode materials for sodium-ion batteries (SIBs), especially for enhancing the specific capacity and cycling stability of anodes, is of great significance for the development of new energy conversion and storage materials. Here, a new type of titanium nitride composite anode (TiN@C) coated with 2D carbon nanosheets was prepared for the first time using a rationally designed topochemical conversion approach of interface-confinement. Subsequently, the electrochemical performance and Na⁺ storage mechanism of TiN@C as an anode for SIBs was investigated. The quantum-dot-sized TiN anodes exhibited shorter ionic transport pathways, while the 2D ultrathin carbon nanosheets reinforced the structural stability of the composite and provided a high electron transformation rate. As a result, the TiN/C composite anode can deliver a high reversible capacity of 170 mA h g^-1 and 149 mA h g^-1 after 5000 cycles at a current density of 0.5 A g^-1 and 1 A g^-1, indicating excellent electrochemical properties. This work provides new opportunities to explore the convenient and controllable preparation of metal nitride anodes for other energy conversion and storage applications.

The integration of bio-catalysis and electrocatalysis to produce fuels and chemicals from carbon dioxide

The dependence on fossil fuels has caused excessive emissions of greenhouse gases (GHGs), leading to climate changes and global warming. Even though the expansion of electricity generation will enable a wider use of electric vehicles, biotechnology represents an attractive route for producing high-density liquid transportation fuels that can reduce GHG emissions from jets, long-haul trucks and ships. Furthermore, to achieve immediate alleviation of the current environmental situation, besides reducing carbon footprint it is urgent to develop technologies that transform atmospheric CO₂ into fossil fuel replacements. The integration of bio-catalysis and electrocatalysis (bio-electrocatalysis) provides such a promising avenue to convert CO₂ into fuels and chemicals with high-chain lengths. Following an overview of different mechanisms that can be used for CO₂ fixation, we will discuss crucial factors for electrocatalysis with a special highlight on the improvement of electron-transfer kinetics, multi-dimensional electrocatalysts and their hybrids, electrolyser configurations, and the integration of electrocatalysis and bio-catalysis. Finally, we prospect key advantages and challenges of bio-electrocatalysis, and end with a discussion of future research directions.

Insight into the effects of calcination temperature on the structure and performance of RuO2/TiO2 in the Deacon process

With an appropriate calcination temperature for preparing a rutile-TiO2 supported RuO2 catalyst, rich surface RuO2 species can be formed on TiO2, leading to its high activity in the oxidation of HCl.

Tuning the shape and crystal phase of TiO2 nanoparticles for catalysis

Synthesis of TiO₂ nanoparticles with tunable shape and crystal phase has attracted considerable attention for the design of highly efficient heterogeneous catalysts. Tailoring the shape of TiO₂, in the crystal phases of anatase, rutile, brookite and TiO₂(B), allows tuning of the atomic configurations on the dominantly exposed facets for maximizing the active sites and regulating the reaction route towards a specific channel for achieving high selectivity. Moreover, the shape and crystal phase of TiO₂ nanoparticles alter their interactions with metal species, which are commonly termed as strong metal-support interactions involving interfacial strain and charge transfer. On the other hand, metal particles, clusters and single atoms interact differently with TiO₂, because of the variation of the electronic structure, while the surface of TiO₂ determines the interfacial bonding via a geometric effect. The dynamic behavior of the metal-titania interfaces, driven by the chemisorption of the reactive molecules at elevated temperatures, also plays a decisive role in elaborating the structure-reactivity relationship.

Influence of ruthenium doping on UV- and visible-light photoelectrocatalytic color removal from dye solutions using a TiO2 nanotube array photoanode

The photocatalytic activity of TiO₂ anodes was enhanced by synthesizing Ru-doped Ti|TiO₂ nanotube arrays. Such photoanodes were fabricated via Ti anodization followed by Ru impregnation and annealing. The X-ray diffractograms revealed that anatase was the main TiO₂ phase, while rutile was slightly present in all samples. Scanning electron microscopy evidenced a uniform morphology in all samples, with nanotube diameter ranging from 60 to 120 nm. The bias potential for the photoelectrochemical (PEC) treatment was selected from the electrochemical characterization of each electrode, made via linear sweep voltammetry. All the Ru-doped TiO₂ nanotube array photoanodes showed a peak photocurrent (PP) and a saturation photocurrent (SP) upon their illumination with UV or visible light. In contrast, the undoped TiO₂ nanotubes only showed the SP, which was higher than that reached with the Ru-doped photoanodes using UV light. An exception was the Ru(0.15 wt%)-doped TiO₂, whose SP was comparable under visible light. Using that anode, the activity enhancement during the PEC treatment of a Terasil Blue dye solution at E_bias(PP) was much higher than that attained at E_bias(SP). The percentage of color removal at 120 min with the Ru(0.15 wt%)-doped TiO₂ was 98% and 55% in PEC with UV and visible light, respectively, being much greater than 82% and 28% achieved in photocatalysis. The moderate visible-light photoactivity of the Ru-doped TiO₂ nanotube arrays suggests their convenience to work under solar PEC conditions, aiming at using a large portion of the solar spectrum.

Comparison study of the effect of CeO2-based carrier materials on the total oxidation of CO, methane, and propane over RuO2

While activity and kinetics of catalytic CO and propane combustion over RuO2 depends sensitively on the carrier material, methane combustion on RuO2 is hardly affected by the carrier.

Climbing with support: scaling the volcano relationship through support–electrocatalyst interactions in electrodeposited RuO2 for the oxygen evolution reaction

The interfacial charge transfer and support-induced electrocatalyst faceting in thin catalysts enable ‘climbing up’ the volcano map for OER electrocatalysts. The conductivity of the support determines the OER activity of thick catalysts.

Controlling CO2 Hydrogenation Selectivity by Metal-Supported Electron Transfer

Tuning CO₂ hydrogenation selectivity to obtain targeted value-added chemicals and fuels has attracted increasing attention. However, a fundamental understanding of the way to control the selectivity is still lacking, posing a challenge in catalyst design and development. Herein, we report our new discovery in ambient pressure CO₂ hydrogenation reaction where selectivity can be completely reversed by simply changing the crystal phases of TiO₂ support (anatase- or rutile-TiO₂ ) or changing metal loadings on anatase-TiO₂ . Operando spectroscopy and NAP-XPS studies reveal that the determining factor is a different electron transfer from metal to the support, most probably as a result of the different extents of hydrogen spillover, which changes the adsorption and activation of the intermediate of CO. Based on this new finding, we can not only regulate CO₂ hydrogenation selectivity but also tune catalytic performance in other important reactions, thus opening up a door for efficient catalyst development by rational design.

Modulating the surface defects of titanium oxides and consequent reactivity of Pt catalysts

In heterogeneous catalysis, it is widely believed that the surface states of catalyst supports can strongly influence the catalytic performance, because active components are generally anchored on supports. This paper describes a detailed understanding of the influence of surface defects of TiO2 supports on the catalytic properties of Pt catalysts. Pt was deposited on reduced (r-), hydroxylated (h-), and oxidized (o-) TiO2 surfaces, respectively, and the different surface states of TiO2 not only lead to differences in metal dispersion, but also distinct electronic interactions between the metal and the support. The highest reactivity for catalytic CO oxidation can be achieved over the Pt catalyst supported on reduced TiO2 with surface oxygen vacancies. The turnover frequency (TOF) of this catalyst is determined to be ∼11 times higher than that of Pt supported on oxidized TiO2. More importantly, the reactivity is seen to increase in the sequence of Pt/o-TiO2 < Pt/h-TiO2 < Pt/r-TiO2, which is well consistent with the trend of the calculated Bader charge of Pt.