Structure-sensitive Reaction Research Articles

Ammonia Decomposition over Ru/SiO2 Catalysts

Ammonia decomposition is a key step in hydrogen production and is considered a promising practical intercontinental hydrogen carrier. In this study, 1 wt.% Ru/SiO2 catalysts were prepared via wet impregnation and subjected to calcination in air at different temperatures to control the particle size of Ru. Furthermore, silica supports with different surface areas were prepared after calcination at different temperatures and utilized to support a change in the Ru particle size distribution of Ru/SiO2. N2 physisorption and transmission electron microscopy were used to probe the textural properties and Ru particle size distribution of the catalysts, respectively. These results show that the Ru/SiO2 catalyst with a high-surface area achieved the highest ammonia conversion among catalysts at 400 °C. Notably, this is closely related to the Ru particle sizes ranging between 5 and 6 nm, which supports the notion that ammonia decomposition is a structure-sensitive reaction.

Heterogeneous enantioselective hydrogenation of an unsaturated carboxylic acid over Pd supported on amine-functionalized silica

The heterogeneous enantioselective hydrogenation of the CC bond of aliphatic α,β-unsaturated carboxylic acids is a key asymmetric catalytic reaction because of its application in the production of pharmaceuticals. In this study, we investigated the enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid over cinchonidine-modified Pd catalysts. To improve the catalytic performance, a support material, mesocellular silica foam (MCF), was functionalized by grafting with primary amines. The use of the amine-functionalized MCF (NH2-MCF) support resulted in enhanced activity and enantioselectivity. The promoting effects originated from the increased electron density of the Pd nanoparticles and the selective blocking of low-coordinated Pd sites by the strong interaction of the amine groups with Pd nanoparticles. Promisingly, the Pd/NH2-MCF catalyst maintained its enantioselectivity over five successive cycles, thus demonstrating the reusability. Our results provide insights into the origin of the promoting effects of amine-functionalized supports and offer a strategy for improving supported catalysts for structure-sensitive reactions.

Synthesized Ni/MMO catalysts via ultrathin Ni-Al-LDH in a rotating packed bed for hydrogenation of maleic anhydride

Fabricating highly active supported Ni-based catalysts is a fundamental challenge in the industry. Herein, the Ni-Al-LDH with controllable thicknesses from 1 to 19 nm were first synthesized to fabricate Ni/MMO catalysts (MMO: Mixed Metal Oxides) using coprecipitation in a rotating packed bed (RPB), followed by hydrothermal aging. It was found that despite the collapse of the sheet-like structure of the ultrathin Ni-Al-LDH during the thermal treatment, the Ni/MMO (designated as 2-NiAl) catalyst obtained from ultrathin Ni-Al-LDH nanosheets (2 nm) possesses the smallest Ni particle size, highest amount of acid sites and surface ratios of Ni/Al among the prepared catalysts. Thus, 2-NiAl demonstrates the optimal activity for the hydrogenation of maleic anhydride (MA), of which the hydrogenation rate is 9.45 (10-3·molMA·gNi-1·min−1, 80 °C, 2 MPa) with ∼100% selectivity to succinic anhydride, higher than most of previous reported values. Moreover, the turnover frequencies as a function of Ni particle sizes demonstrate a linear correlation, indicating that MA hydrogenation is a structure-sensitive reaction. These results provide a new route to optimize the catalytic performance of Ni-based catalysts and a guidance for designing catalysts derived from LDH for hydrogenation reactions. Furthermore, the prepared 2-NiAl catalyst is a potential catalyst for hydrogenation of MA into SA in the industry.

Insight into the critical role of strong interaction between Ru and Co in RuCo single-atom alloy structure for significant enhancement of ammonia synthesis performance

Rational design of efficient catalysts for ammonia (NH3) synthesis at mild conditions is of paramount importance for the development of electrolysis driven Haber-Bosch (eHB) process. Ammonia synthesis is a structure sensitive reaction, and any small change of electronic structure could result in dramatic change of catalytic activity, especially for the Ru-based NH3 synthesis catalysts. Electronic structure modulation of the Ru-based catalysts could provide desirable catalytic activity. Herein, we explore a class of Ru-Co single-atom alloy catalysts (marked as RuxCo1 SAA, x stands for Ru/Co molar ratio), in which Co single atoms are located on Ru nanoclusters to form Co-Ru coordination, and then electronic structure of RuxCo1 SAA could be effectively tuned by regulating the Ru/Co molar ratio. Our studies show that a moderate ratio of Ru/Co (1.7:1) favors superior NH3 synthesis rate and low activation energy. Using a suite of elaborate characterizations, we have observed that the outstanding performance over Ru1.7Co1 SAA can be attributed to the electron redistribution between Ru and Co atom, resulting in an upshift of d band center and lowering of work function. However, there is decrease of NH3 synthesis rate when Ru/Co molar ratio is 2, due to the partial detachment of Ru entities from SAA structure, and the formed individual Ru nanoparticles (NPs) overlay the surface of catalyst. In such a case, N2 activation behavior over Ru2Co1 is alike that of Ru NPs catalysts. The present study demonstrates that the Ru/Co ratio in SAA structure can effectively regulate the electronic structure of catalyst for NH3 synthesis rate enhancement.

Insight into the structural sensitivity of CuZnAl catalysts for CO hydrogenation to alcohols

The catalytic conversion of CO hydrogenation is a structure-sensitive reaction over Cu-based catalyst. It is very important to distinguish the structural differentiation and possible reaction pathway of Cu-based catalysts in methanol synthesis and ethanol/C2+OH synthesis. Herein, the activity of four types of CuZnAl catalysts is evaluated, and their structural differentiation is investigated. The CuZnAl catalyst (CZA) prepared by a complete liquid-phase (CLP) method after solid–liquid separation directly applied in the fixed bed reactor also shows the ability to synthesize ethanol and higher alcohols (C2+OH), with the selectivity of C2+OH in liquid product reaching up to 31.6% at the CO conversion of 10.6%. However, commercial methanol synthesis catalyst (CMC) displays the highest CO conversion (28.2%) and the poorest C2+OH selectivity (7.8%). After characterized by ICP, XRD, CO-TPD, N2O adsorption, XPS, SEM, TEM and in-situ DRIFTS techniques, it is discovered that the dispersion of Cu and the exposed Cu surface area significantly influences CO conversion. The selectivity of ethanol and C2+OH is related to the size and distribution of Cu, the architectural feature, and the chemical environment of Cu and Al. In-situ DRIFTS indicates that CHxO* species can be formed over different CuZnAl catalysts. However, the formed CHxO* species will be rapidly hydrogenated to produce methanol on CMC catalyst, while the step is inhibited on CZA catalyst. Additionally, a bridge-type adsorbed CO is only observed on CZA catalyst, which is beneficial for the formation of CHx intermediates, leading to the formation of ethanol and higher alcohols.

Size-dependent activity of supported Ru catalysts for ammonia synthesis at mild conditions

Ammonia (NH3) synthesis is a structure-sensitive reaction, where a minute variation of catalyst structure would lead to a dramatic change of activity. To date, the roles of Ru size on NH3 synthesis still remain elusive, and it remains a major challenge. Herein, a series of Ru catalysts with sizes ranging from 1.4 to 5.0 nm were prepared by colloidal Ru deposition, which allows the investigation of size influence on NH3 synthesis. Through analyses of the geometric and electronic properties of variable-sized Ru particles, it shows that the reduction of Ru particle size could increase the proportion of corner sites while decrease that of terrace sites, which can decrease the work function and thus promote N2 for its activation. Isotopic investigations show that the decrease of dissociative contribution but the increase of associative contribution as Ru particle size was decreased from 5.0 to 1.4 nm. Meanwhile, the NH3 synthesis rate increases when the size of Ru catalysts decreases from 5.0 to 1.4 nm. Using a suite of elaborate characterizations, we have observed that 1.4 nm Ru nanoclusters (NCs) with ample corner sites are conducive to activate N2 via an associative route. As a result, the 1.4 nm Ru NCs catalyst shows the highest NH3 synthesis rate (up to 17.13 mmolNH3 gcat−1h−1) at 400 ℃ and 1 MPa.

Manipulating the interfacial species on carbon nanospheres supported nanoparticulate Ru to boost the electronic metal−support interaction for enhancing selective hydrogenation of levulinic acid

Interfacial synergistic catalysis of supported metallic catalysts via engineering the electronic metal−support interaction (EMSI), i.e., manipulating the electronic/geometric configuration of interfacial sites, is an efficient strategy to promote their performances in structure-sensitive reactions, such as selective hydrogenation of levulinic acid (SHLA) to γ-valerolactone (GVL). Herein, carbon nanospheres (CNSs) with controlled morphology and tunable contents of surface carbonaceous species were facilely fabricated to support Ru nanoparticles (NPs). Combined with spectroscopic and microscopy characterizations, the EMSI between Ru and the special C = O species on interface of the Ru/CNSs catalysts was recognized, which contributed to the formation of small-sized Ru NPs with interfacial electron-deficient Ru (Ruδ+) sites. Such modulated electronic configuration of interfacial sites facilitated the H2 adsorption strength and capacity, eventually lowering the apparent activation energy (Ea) and boosting the intrinsic activity of Ru/CNSs in SHLA. A linearity between the turnover frequencies (TOFs) of levulinic acid (LA) and the contents of C = O species was demonstrated, substantiating the interfacial synergistic catalysis-mediated activity promotion evoked by enhancing the EMSI on Ru/CNSs.

Size-Controlled Nanoparticles Embedded in a Mesoporous Architecture Leading to Efficient and Selective Hydrogenolysis of Polyolefins.

A catalytic architecture, comprising a mesoporous silica shell surrounding platinum nanoparticles (NPs) supported on a solid silica sphere (mSiO2/Pt-X/SiO2; X is the mean NP diameter), catalyzes hydrogenolysis of melt-phase polyethylene (PE) into a narrow C23-centered distribution of hydrocarbons in high yield using very low Pt loadings (∼10-5 g Pt/g PE). During catalysis, a polymer chain enters a pore and contacts a Pt NP where the C-C bond cleavage occurs and then the smaller fragment exits the pore. mSiO2/Pt/SiO2 resists sintering or leaching of Pt and provides high yields of liquids; however, many structural and chemical effects on catalysis are not yet resolved. Here, we report the effects of Pt NP size on activity and selectivity in PE hydrogenolysis. Time-dependent conversion and yields and a lumped kinetics model based on the competitive adsorption of long vs short chains reveal that the activity of catalytic material is highest with the smallest NPs, consistent with a structure-sensitive reaction. Remarkably, the three mSiO2/Pt-X/SiO2 catalysts give equivalent selectivity. We propose that mesoscale pores in the catalytic architecture template the C23-centered distribution, whereas the active Pt sites influence the carbon-carbon bond cleavage rate. This conclusion provides a framework for catalyst design by separating the C-C bond cleavage activity at catalytic sites from selectivity for chain lengths of the products influenced by the structure of the catalytic architecture. The increased activity, selectivity, efficiency, and lifetime obtained using this architecture highlight the benefits of localized and confined environments for isolated catalytic particles under condensed-phase reaction conditions.

Few-Atom Pt Ensembles Enable Efficient Catalytic Cyclohexane Dehydrogenation for Hydrogen Production.

Identification of catalytic active sites is pivotal in the design of highly effective heterogeneous metal catalysts, especially for structure-sensitive reactions. Downsizing the dimension of the metal species on the catalyst increases the dispersion, which is maximized when the metal exists as single atoms, namely, single-atom catalysts (SACs). SACs have been reported to be efficient for various catalytic reactions. We show here that the Pt SACs, although with the highest metal atom utilization efficiency, are totally inactive in the cyclohexane (C6H12) dehydrogenation reaction, an important reaction that could enable efficient hydrogen transportation. Instead, catalysts enriched with fully exposed few-atom Pt ensembles, with a Pt-Pt coordination number of around 2, achieve the optimal catalytic performance. The superior performance of a fully exposed few-atom ensemble catalyst is attributed to its high d-band center, multiple neighboring metal sites, and weak binding of the product.

Competition between reverse water gas shift reaction and methanol synthesis from CO2: influence of copper particle size.

Converting CO2 into value-added chemicals and fuels, such as methanol, is a promising approach to limit the environmental impact of human activities. Conventional methanol synthesis catalysts have shown limited efficiency and poor stability in a CO2/H2 mixture. To design improved catalysts, crucial for the effective utilization of CO2, an in-depth understanding of the active sites and reaction mechanism is desired. The catalytic performance of a series of carbon-supported Cu catalysts, with Cu particle sizes in the range of 5 to 20 nm, was evaluated under industrially relevant temperature and pressure, i.e. 260 °C and 40 bar(g). The CO2 hydrogenation reaction exhibited clear particle size effects up to 13 nm particles, with small nanoparticles having the lower activity, but higher methanol selectivity. MeOH and CO formation showed a different size-dependence. The TOFCO increased from 1.9 × 10-3 s-1 to 9.4 × 10-3 s-1 with Cu size increasing from 5 nm to 20 nm, while the TOFMeOH was size-independent (8.4 × 10-4 s-1 on average). The apparent activation energies for MeOH and CO formation were size-independent with values of 63 ± 7 kJ mol-1 and 118 ± 6 kJ mol-1, respectively. Hence the size dependence was ascribed to a decrease in the fraction of active sites suitable for CO formation with decreasing particle size. Theoretical models and DFT calculations showed that the origin of the particle size effect is most likely related to the differences in formate coverage for different Cu facets whose abundancy depends on particle size. Hence, the CO2 hydrogenation reaction is intrinsically sensitive to the Cu particle size.

Comparing interfacial cation hydration at catalytic active sites and spectator sites on gold electrodes: understanding structure sensitive CO2 reduction kinetics.

Hydrated cations present in the electrochemical double layer (EDL) are known to play a crucial role in electrocatalytic CO2 reduction (CO2R), and numerous studies have attempted to explain how the cation effect contributes to the complex CO2R mechanism. CO2R is a structure sensitive reaction, indicating that a small fraction of total surface sites may account for the majority of catalytic turnover. Despite intense interest in specific cation effects, probing site-specific, cation-dependent solvation structures remains a significant challenge. In this work, CO adsorbed on Au is used as a vibrational Stark reporter to indirectly probe solvation structure using vibrational sum frequency generation (VSFG) spectroscopy. Two modes corresponding to atop adsorption of CO are observed with unique frequency shifts and potential-dependent intensity profiles, corresponding to direct adsorption of CO to inactive surface sites, and in situ generated CO produced at catalytic active sites. Analysis of the cation-dependent Stark tuning slopes for each of these species provides estimates of the hydrated cation radius upon adsorption to active and inactive sites on the Au electrode. While cations are found to retain their bulk hydration shell upon adsorption at inactive sites, catalytic active sites are characterized by a single layer of water between the Au surface and the electrolyte cation. We propose that the drastic increase in catalytic performance at active sites stems from this unique solvation structure at the Au/electrolyte interface. Building on this evidence of a site-specific EDL structure will be critical to understand the connection between cation-dependent interfacial solvation and CO2R performance.

Dynamic restructuring of supported metal nanoparticles and its implications for structure insensitive catalysis

Some fundamental concepts of catalysis are not fully explained but are of paramount importance for the development of improved catalysts. An example is the concept of structure insensitive reactions, where surface-normalized activity does not change with catalyst metal particle size. Here we explore this concept and its relation to surface reconstruction on a set of silica-supported Ni metal nanoparticles (mean particle sizes 1–6 nm) by spectroscopically discerning a structure sensitive (CO2 hydrogenation) from a structure insensitive (ethene hydrogenation) reaction. Using state-of-the-art techniques, inter alia in-situ STEM, and quick-X-ray absorption spectroscopy with sub-second time resolution, we have observed particle-size-dependent effects like restructuring which increases with increasing particle size, and faster restructuring for larger particle sizes during ethene hydrogenation while for CO2 no such restructuring effects were observed. Furthermore, a degree of restructuring is irreversible, and we also show that the rate of carbon diffusion on, and into nanoparticles increases with particle size. We finally show that these particle size-dependent effects induced by ethene hydrogenation, can make a structure sensitive reaction (CO2 hydrogenation), structure insensitive. We thus postulate that structure insensitive reactions are actually apparently structure insensitive, which changes our fundamental understanding of the empirical observation of structure insensitivity.

Correlations between properties and activity of platinum supported on modified carbon nanotubes with pyridines

Using chemically modified supports is a strategy to differentiate metal deposition, catalyst morphology and properties and, ultimately, the electrochemical activity towards the multiparametric and structure-sensitive Oxygen Reduction Reaction (ORR). Functionalized carbon nanotubes with pyridine groups, oxpyMWCNT, is a support that allows fine spatial dispersion of nanoparticles. This work reports the development of Pt supported on oxpyMWCNT with different metal loadings using the polyol method in alkaline reaction media. The effect of the pH value of the reaction solution and the reduction time on the deposition, the morphological and surface characteristics of the formed electrocatalysts was thoroughly investigated. The electrochemical performance of the aforementioned electrocatalysts towards ORR was evaluated. By using the aforementioned support, small particle size and fine and homogeneous dispersion were achieved that allowed the correlation between the properties and the electrocatalytic activity. Thus, there is a discussion about how mass and specific activity towards ORR are simultaneously affected by metal-support interactions, interparticle distance (particle proximity) and nanoparticle size.

First-principles insights into ammonia decomposition on WC (0001) surface terminated by W and C

In order to investigate the adsorption and dehydrogenation process of ammonia on WC (0001) surfaces terminated by W and C atoms, the density functional theory (DFT) was used along with periodic slab models. All possible adsorption configurations and energies of relevant intermediates on WC (0001) surfaces were identified. The results of the adsorption energy and transition states showed that the C-terminated WC surface was more favorable for hydrogen production by the decomposition of ammonia. Conversely, the WC surface terminated by W atoms was susceptible to be poisoned by the adsorbed N atoms, leading to the combinative desorption of N atoms as the rate-limiting step in the entire reaction. The unique differences between WC (0001) surfaces terminated by W and C atoms suggested that a structure-sensitive reaction was ammonia decomposition over the WC catalyst.

Hydrodeoxygenation of 2,5-dimethyltetrahydrofuran over bifunctional metal-acid catalyst Pt–Cs2.5H0.5PW12O40 in the gas phase: Kinetics and mechanism

• DMTHF deoxygenated to hexane with >99% selectivity at 90–100 °C and ambient pressure. • Bifunctional Pt–CsPW catalyst much more efficient than monofunctional pt. • HDO occurs via hydrogenolysis, dehydration and hydrogenation steps on pt and H + sites. • Hydrogenolysis of furan ring on pt is a structure-sensitive reaction. Hydrodeoxygenation (HDO) of 2,5-dimethyltetrahydrofuran (DMTHF) was studied at a gas-solid interface in a fixed-bed microreactor in the presence of bifunctional metal-acid catalysts comprising Pt/C and acidic heteropoly salt Cs 2.5 H 0.5 PW 12 O 40 (CsPW). The Pt–CsPW catalyst deoxygenated DMTHF to n-hexane with >99% selectivity under mild conditions (90–100 °C, ambient pressure) and was much more efficient than monofunctional Pt/C. On the basis of kinetic studies, a mechanism for the HDO of DMTHF over Pt–CsPW was proposed, which includes a sequence of hydrogenolysis, dehydration and hydrogenation steps catalysed by Pt and proton sites of the bifunctional catalyst. The turnover rate of HDO increased with increasing Pt particle size suggesting that the hydrogenolysis of C–O bond in furanic compounds on Pt is a structure-sensitive reaction.

Enhanced catalytic performance of Pd nanoparticles during propane dehydrogenation by germanium promotion

Germanium has emerged recently as a potential promoter for Pt-based catalysts for propane dehydrogenation (PDH) . However, its general practicality with other noble metals remains unexplored. Herein, the catalytic performance of Pd-Ge/SiO2 was investigated in propane dehydrogenation (PDH), wherein a significant improvement of the catalytic performance was obtained by Ge addition. Pd2/SiO2, the unpromoted sample, shows an initial conversion and selectivity of 21.0% and 53.6% at 550 °C, respectively. In addition, it deactivates rapidly with a deactivation constant (kd) of 1.7 × 10−2 min−1. Ge-promoted samples exhibit a slight decrease in activity, while catalyst selectivity and stability significantly increase. Upon adding 1 wt.% Ge (Pd2-Ge1/SiO2), the initial conversion decreases to 15.2%, whereas the initial selectivity increases to 91.9%. Further addition of Ge (2 wt.%, Pd2-Ge2/SiO2) leads to an initial conversion of 12.5% and an initial selectivity of 95.0%. Regarding catalyst stability, the deactivation constant is almost one order of magnitude lower for Ge-promoted catalysts (i.e., with 1 wt.% and 2 wt.% Ge); 2.9 × 10−3 min−1 and 2.0 × 10−3 min−1, respectively. The characterization results indicate that Ge imposes geometric and electronic modifications on Pd, decreasing catalytic activity for structure-sensitive side reactions and facilitating propylene desorption from surface. Hence, both the selectivity and stability of the catalysts have been significantly enhanced.

Efficient direct deoxygenation of bio-oil model compound (anisole) on highly dispersed SiO2-supported Ni3Ga intermetallic compound prepared by direct impregnation-reduction method

SiO2 supported Ni3Ga intermetallic compound (IMC) with different nominal Ni contents (x%Ni3Ga/SiO2) were prepared by the simple impregnation-reduction method and evaluated for the hydrodeoxygenation of anisole (a representative bio-oil model compound) on a fix-bed reactor at 300 °C and 0.1 MPa. Different from the case that the calcination led to large NiO particle after the impregnation, nickel silicate rather than NiO were found without calcination. This results in highly dispersed Ni3Ga IMC crystallites after the reduction. Nevertheless, the decrease of Ni3Ga IMC crystallites size did not affect the electronic interaction between Ni and Ga and the surface Ni/Ga atomic ratio. Interestingly, the Ni3Ga particles size (~5.0 nm) did not become large with increasing the nominal Ni contents from 5% to 20%. Also, the spilt-over hydrogen species on x%Ni3Ga/SiO2 were more easily desorbed than those on the catalyst via the calcinaiton. Consequently, x%Ni3Ga/SiO2 gave higher reactivity in the direct deoxygenation of anisole to benzene. Given the turnover frequency (TOF) of anisole was affected by the Ni3Ga crystallites size, we suggest that the HDO of anisole on Ni3Ga/SiO2 was structure sensitive reaction. With increasing the nominal Ni content, there was an optimal performance on 15%Ni3Ga/SiO2, where the conversion of anisole and the selectivity to benzene reached as high as 94.9% and 94.5%, respectively, remarkably higher than those (51.4% and 87.2%) on the Ni3Ga/SiO2 prepared catalyst by the impregnation-calcination-reduction method.

Copper Single-Atom-Covered Pt Nanoparticles for Selective Hydrogenation of Phenylacetylene

The selective hydrogenation of alkynes to alkenes is very important for both industry and scientific investigation, and overhydrogenation of alkynes to alkanes is the biggest problem to be solved. Suppressing the catalytic hydrogenation of alkenes to alkanes and keeping the efficient conversion from alkynes to alkenes at the same time is a viable solution, but the slight difference in structure between alkynes and the corresponding alkenes causes great difficulty in realizing such a target. The Pt/C–Cu bimetallic catalysts are used to catalyze the selective hydrogenation of phenylacetylene (PA) to styrene (ST). High-resolution STEM and EXAFS results show that the prepared Pt/C–Cu catalysts are composed of copper single atoms and Pt nanoparticles. In particular, Pt/C–Cu is a catalyst in which copper single atoms cover the surface of Pt nanoparticles. The experimental results reveal that the selectivity of ST strongly depends on the coverage of Cu single atoms over Pt nanoparticles in Pt/C–Cu, so selective hydrogenation of PA is a structure-sensitive reaction. The selectivity of ST can reach 94.4% at a PA conversion of 100% in the selective hydrogenation of PA over Pt/C–0.5Cu, an optimized Pt–Cu bimetallic catalyst; after selective removal of PA in ST from 100 to 30 ppm over the same catalyst, the yield of ST reaches 99.97%. The chemisorption results of H2 and probe molecule ethene (C2H4) over the Pt–Cu/C catalysts reveal that Cu single atoms covering on the surface of Pt nanoparticles weaken the Pt–H and Pt–C2H4 interactions, so the catalytic hydrogenation of the carbon–carbon double bond over Pt/C–0.5Cu can be tremendously suppressed. The added Cu single atoms over Pt nanoparticles are not poisonous sites because they can also act as the active centers to activate hydrogen and the carbon–carbon double bond.

Designing Active Sites for Structure-Sensitive Reactions via the Generalized Coordination Number: Application to Alcohol Dehydrogenation

Identifying the structure of the most active site is essential to improve the performance of supported metal catalysts. For structure-sensitive reactions, in silico design cannot be easily achieved combining the scaling relations and Bronsted–Evans–Polanyi relations, which are only built on energy-based descriptors. We used here the generalized coordination number as a structural descriptor and established that low-coordinated sites are desirable when using Co and Cu to perform the acceptor-less alcohol dehydrogenation reaction.

Nanoparticulate Ru on morphology-manipulated and Ti3+ defect-riched TiO2 nanosheets for benzene semi-hydrogenation

The catalytically reactive defects act a pivotal role in enhancing the performances toward structure-sensitive reactions, such as benzene semi-hydrogenation (BSH). Herein, massive Ti3+ defects, recognized by multiple spectroscopic technics, were effectively implanted into brookite TiO2 nanosheets (BTNSs) enclosed by {1 0 1}, {2 0 1}, and {2 1 0} facets. The content of these defects, expressed by Ti3+: Ti4+ molar ratio, increased from 0.44 to 1.19 when the hydrothermal time of BTNSs prolonged from 1 to 12 h, and then decreased to 1.04 at 48 h. Benefited by such an integration of the unique microscopic architecture and atomic-scale defects, the BTNSs supported nanoparticulate Ru catalysts exhibited an increased metal size but a decreased acid amount accompanying with the extension of hydrothermal time, which synergistically determined that the Ru/BTNSs-2 catalyst with favorable Ru size and acid amount occupied the highest turnover frequency (TOF) of benzene (127.5 min−1). Meanwhile, the Ti3+ defects provided both improved net rate of cyclohexene generation and enhanced suppression of cyclohexene adsorption, resulting in a positive linearity between the initial cyclohexene selectivity (S0) and Ti3+: Ti4+ molar ratio over the Ru/BTNSs catalysts. A maximum S0 of 90.3% was achieved on the Ru/BTNSs-12 catalyst with most Ti3+ defects, outperforming the previous TiO2-supported Ru catalysts.