Initial TOF Research Articles

Hydrogen Production from the Decomposition of Formic Acid over Carbon Nitride‐Supported AgPd Alloy Nanoparticles

AbstractHighly dispersed bimetallic AgPd alloy nanoparticles with various ratios have been supported on carbon nitride by using a co‐reduction method and then tested for catalytic dehydrogenation of formic acid without base addictive. It was found that the activity of the catalyst depended directly on the AgPd ratios of the catalyst and the reaction temperature. The Ag1Pd2/CN catalyst exhibited excellent catalytic activity for hydrogen generation from formic acid with the initial TOF of 621 h−1 at 348 K. The synergetic interaction between the bimetallic AgPd nanoparticles and the carbon nitride support, the AgPd ratio and the dispersion of AgPd nanoparticles on the support contribute to the high catalytic performance of the AgPd/CN catalysts.

High-performance graphite-supported ruthenium nanocatalyst for hydrogen evolution reaction

The monodisperse graphite supported ruthenium (0) nanoparticles (Ru (0)/Graphite NPs) was obtained by using chemical reduction method and performed in the dehydrogenation reaction of dimethyl-amine borane (DMAB). The characterization of Ru (0)/Graphite NPs was characterized by Transmission Electron Microscopy (TEM), High-Resolution Transmission Electron Microscopy (HRTEM), X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), and Raman Spectroscopy. After full characterization of Ru (0)@Graphite NPs, the prepared nanoparticles were performed for the catalytic dehydronation of dimethylamine borane and it has been found that Ru (0)/Graphite NPs is a highly active catalyst for this purpose. The initial TOF value was found to be 281.51 h−1 at ambient conditions. Ru (0)/Graphite NPs were also tried for reusability and durability measurements and it was found that Ru (0)/Graphite NPs maintained their catalytic activities with the beginning performance of 79% during the dehydrogenation of DMAB. In addition, the detailed kinetic studies were investigated depending on the concentration of catalyst, temperature and etc. The results showed that the activation enthalpy (ΔH#), entropy (ΔS#) and energy (Ea) were found to be 11.33 kJ·mol−1, −220.686 J mol−1 K−1, and 13.82 kJ·mol−1, respectively, for the dehydrogenation of DMAB.

Hydrogen-generating behavior of Pd-decorated gold nanoparticles via formic acid decomposition

Formic acid is a promising hydrogen storage material where hydrogen is generated via metal-catalyzed decomposition. Bimetallic catalysts are active for this reaction, but the mechanism has not been fully proven. Palladium metal supported on gold nanoparticles (Pd-on-Au NPs) has structural properties that are advantageous for studying aqueous-phase catalytic reactions. In this work, a series of Pd-on-Au NPs of varying Pd loadings (calculated in terms of Pd surface coverage, sc%) were synthesized, immobilized onto carbon, and studied for formic acid decomposition at room temperature. Pd-on-Au NPs were catalytically active, with a reaction rate constant as high as 137 m L-H2/gPd/min (corresponding to an initial turnover frequency TOF of 123 h−1) at a Pd loading of 300 sc%. In contrast, Au NPs were inactive, and Pd NPs were slightly active (5 mL-H2/gPd/min and TOF of 38 h−1). The Pd metal of Pd-on-Au catalysts are partially oxidized, and is readily reduced without changing the metal-on-metal structure during reaction, according to in situ x-ray adsorption spectroscopy measurements. CO formation was inhibited at a Pd loading of 300 sc%, suggesting that three-dimensional Pd ensembles favored the desired dehydrogenation pathway while single-atom and small two-dimensional Pd ensembles are active for the undesired dehydration pathway.

Insights on palladium decorated nitrogen-doped carbon xerogels for the hydrogen production from formic acid

N-doped carbon xerogels synthesized from melamine-resorcinol-formaldehyde aqueous gels were used as supports for the preparation of Pd-based catalysts for the formic acid dehydrogenation reaction. The effect of the pore texture and nitrogen content of the carbon xerogels on the catalytic activity for the hydrogen production was investigated. It was observed that an appropriate nitrogen doping in a well-defined micro-mesoporous carbon xerogel enables the preparation of Pd catalysts with appreciable catalytic enhancement towards the formic acid dehydrogenation as compared to the N-free counterpart, reaching an initial TOF value of 2014 h−1.

Interconversion between CO2 and HCOOH under Basic Conditions Catalyzed by PdAu Nanoparticles Supported by Amine-Functionalized Reduced Graphene Oxide as a Dual Catalyst

Recently, the utilization of formic acid (FA) or formate as promising hydrogen carriers through the interconversion between CO2 and HCOOH or HCO3– and HCOO–, respectively, has attracted increasing research interest. In this work, a PdAu bimetallic catalyst supported on phenylenediamine-alkalized reduced graphene oxide (Pd0.50Au0.50/PDA-rGO) was developed for catalyzing bicarbonate hydrogenation under basic conditions as well as FA/formate dehydrogenation under acidic and basic conditions. Without any additives, a very high yield (94%) of potassium formate (PF) can be achieved from the hydrogenation of potassium bicarbonate at 50 °C for 16 h. On the other hand, initial TOFs of 1.63 × 103 and 6.98 × 103 h–1 were accomplished in the dehydrogenations of 6 mol/L PF and 8 mol/L FA, respectively, at 80 °C. This work successfully demonstrates highly efficient CO2 hydrogenation and is the first report of a Pd-based heterogeneous catalyst for the additive-free dehydrogenation of concentrated (>6 mol/L) PF or FA sol...

Progression of late postoperative atrial fibrillation in patients with tetralogy of Fallot.

ToF patients are at risk for ventricular deterioration at a relatively young age, which can be aggravated by AF development. Therefore, knowledge on AF development and its timespan of progression is essential to guide treatment strategies for AF. We examined late postoperative AF onset and progression in ToF patients during long-term follow-up after ToF correction. In addition, coexistence of AF with regular supraventricular tachyarrhythmias (SVT) and ventricular tachyarrhythmias (VTA) was analyzed. ToF patients (N=29) with AF after ToF correction referred to the electrophysiology department between 2000 and 2015 were included. All available rhythm registrations were reviewed for AF, regular SVT, and VTA. AF progression was defined as transition from paroxysmal AF to (longstanding) persistent/permanent AF or from (longstanding) persistent AF to permanent AF. At the age of 44 ± 12 years, ToF patients presented with paroxysmal (N=14, 48%), persistent (N=13, 45%) or permanent AF (N=2, 7%). Age of AF development was similar among patients who either underwent initial shunt creation (N=15, 45 ± 11 [25-57] years) or primary total ToF correction (N=14, 43 ± 13 [26-66] years) (P=0.785). AF coexisted with regular SVT (N=18, 62%) and VTA (N=13, 45%). Progression of AF occurred in 11 patients (38%) within 5 ± 5 years after AF onset despite antiarrhythmic drug class II (AAD, P=0.052) or III (P=0.587) usage. AF in our ToF population developed at a young age and showed rapid progression. Rhythm control by pharmacological therapy was ineffective in preventing AF progression.

Highly Active and Readily Accessible Proline-Based Dizinc Catalyst for CO2 /Epoxide Copolymerization.

In the pursuit of CO2 -based materials, the development of efficient catalysts for the alternating copolymerization of CO2 and epoxides to give polycarbonates is receiving particular attention. Desirable attributes for such catalysts are high copolymerization activity at low CO2 pressure, as well as chemo- and stereocontrol over the formed polymer. Here, we report a novel chiral zinc catalyst that can be isolated in 97 % yield from commercial sources, and that produces polycarbonates selectively from neat cyclohexene oxide under 1 bar of CO2 pressure at temperatures above 50 °C. At 80 °C reaction temperature, TONs of 1684 and initial TOFs up to 149 h-1 were measured, producing an isotactic-enriched polycarbonate with a probability Pm of 65 % for the formation of a meso diad. Insight into the dinuclear nature of the active species and the copolymerization progress has been gained from structural and spectroscopic studies.

A Single Organoiridium Complex Generating Highly Active Catalysts for both Water Oxidation and NAD+/NADH Transformations

The complex [Cp*Ir(pica)Cl] (1; pica = picolinamidate = κ2-pyridine-2-carboxamide) was found to be an effective catalyst for both water oxidation to molecular oxygen and NAD+/NADH transformations, which are the key reactions of light-dependent natural photosynthesis. In particular, 1 exhibits high activity in water oxidation driven by CAN and NaIO4. With the former, the initial TOF exceeds that of [Cp*Ir(pic)Cl] (2; pic = picolinate = κ2-pyridine-2-carboxylate), which is the fastest iridium catalyst reported to date, whereas with NaIO4 it compares well with the best catalysts. 1 exhibits top performances also in the hydrogenation of NAD+ with HCOOK, leading to the regiospecific formation of 1,4-NADH (pH 7) with TOF = 143 h–1, which is about 3 times higher than the previous highest value (54 h–1) reported for [Cp*Ir(4-(1H-pyrazol-1-yl-κN2)benzoic acid)(H2O)]SO4 (3). The activity seems to be critically affected by the presence of the NH functionality, as indicated by its drop of about 1 order of magnitude w...

Asymmetric Transfer Hydrogenation of Ketones Using New Iron(II) (P‐NH‐N‐P′) Catalysts: Changing the Steric and Electronic Properties at Phosphorus P′

AbstractThe asymmetric transfer hydrogenation (ATH) of ketones is an efficient method for producing enantio‐enriched alcohols which are used as intermediates in a variety of industrial processes. Here we report the synthesis of new iron ATH precatalysts (S,S)‐[FeBr(CO)(Ph2PCH2CH2NHCHPhCHPhNC=CHCH2PR′2)][BPh4] (R′=Et, and ortho‐tolyl (o‐Tol)) where one of the phosphine groups is modified with small alkyl and large aryl substituents to probe the effect of this change on the activity and selectivity of the catalytic system. A simple reversible equilibrium kinetic model is used to obtain the initial TOF and the inherent enantioselectivity S=kR/kS of these catalysts along with those for the previously reported catalysts with R′=Ph and Cy for the ATH of acetophenone. With an increase in the size of the PR′2 group, the TOF goes through a maximum at PPh2 while the S value goes through a maximum of 510 at R′=Cy. The complex with R′=o‐Tol starts with a high S value of 200 but is rapidly changed to a second catalyst with an S value of 28. For the reduction of acetophenone to (R)‐1‐phenylethanol, turnover numbers of up to 5200 and ee up to 98 % were achieved. The chemotherapeutic pharmaceutical precursor (R)‐(3′,5′‐bis(trifluoromethyl))‐1‐phenylethanol is synthesized in up to 95 % ee. Several other alcohols can be prepared in greater than 90 % ee by choosing the precatalyst with the correctly matched steric properties. A hydride complex derived from the catalyst with R′=Cy is characterized by NMR spectroscopy. It is proposed that low concentration trans‐hydride carbonyl complexes with the FeH parallel to the NH of the ligand are the active catalysts in all of these systems.

Sub 1 nm aggregation-free AuPd nanocatalysts confined inside amino-functionalized organosilica nanotubes for visible-light-driven hydrogen evolution from formaldehyde

Novel amino-functionalized organosilica nanotubes (AM-NT) were facilely synthesized by the hydrolysis and co-condensation of 3-aminopropyltrimethoxysilane (APTMS) with 1,4-bis(triethoxysilyl)benzene (BTEB) using a simple micelle-templating approach. Through adjusting the ratios of organosilane precursors, the very short AM-NT with ∼60nm in length and ∼6nm in pore diameter could be controllably obtained. By using the unique AM-NT as the supports, a series of AuPd alloy nanoparticles with the average size of sub 1nm could be synthesized after the liquid phase reduction of HAuCl4 and H2PdCl4 in water, which were mostly confined inside the short organosilica nanotubes and further applied for the hydrogen evolution from formaldehyde aqueous solution. These bimetallic AuPd nanocatalysts in the organic-modified nanotubes exhibited remarkably improved catalytic activity under visible light irradiation and the highest initial TOF value of 241.7h−1 could be achieved at the room temperature. Furthermore, these ultrasmall nanocatalysts exhibited high reaction stability and no aggregation of metal nanoparticles was observed even after 5 recycles. The superior catalytic activity was mainly attributed to the uniform and ultrafine AuPd nanostructure, benefiting from the synergetic stabilizing effects of amino and benzene groups in the nanotube frameworks. The fast electron transfer from much smaller Au with localized surface plasmon resonance (LSPR) to active Pd sites could efficiently occur, resulting in the excellent photocatalytic activity.

In Situ Formed Fe Cation Modified Ir/MgO Catalyst for Selective Hydrogenation of Unsaturated Carbonyl Compounds

Selective hydrogenation of α,β-unsaturated ketones to α,β-unsaturated secondary alcohols is a challenging reaction for heterogeneous catalysts because of the nonuniformity of their surface active sites, and high-yield synthesis of the target α,β-unsaturated secondary alcohols has not been achieved by heterogeneous catalysts. Herein, we found that Fe cation modified Ir/MgO acted as an effective heterogeneous catalyst for the reaction, providing high yield (up to 90%) of α,β-unsaturated secondary alcohols. The activity is high (initial TOF = 12 min–1 and TOFs (TOF per surface Ir site) = 84 min–1), and the TOF is more than 10 times higher than those of the reported heterogeneous catalysts. To the best of our knowledge, the TOFs is the highest among the reported homogeneous and heterogeneous catalysts under additional base-free conditions. The catalyst was easily fabricated by only mixing Ir/MgO and Fe cation precursor in the reaction media, and the active sites were proposed to be the interface among Ir meta...

Highly dispersed Pd-MnOx nanoparticles supported on graphitic carbon nitride for hydrogen generation from formic acid-formate mixtures

Highly dispersed Pd and MnOx nanoparticles supported on the graphitic carbon nitride with different composition have been prepared by a simple liquid deposition-reduction method and used as an efficient FA decomposition catalyst for hydrogen generation. The catalytic activity depends on the Pd-MnOx composition of catalyst, the FA/SF ratio and the reaction temperature. The Pd-MnOx/CN-1 catalyst exhibited excellent catalytic activity for hydrogen generation with the initial TOF of 465 h−1 from formic acid-sodium formate mixture aqueous solution with a FA/SF ratio of 1:8 at 348 K. The synergetic effect between Pd nanoparticles and the carbon nitride support, the Mn/Pd ratios, the good dispersion of nanoparticles and the nature of the carbon nitride support were suggested to be responsible for the efficient catalytic performance of the Pd-MnOx/CN nanocatalysts.

The impact of support surface area on the SMSI decoration effect and catalytic performance for Fischer-Tropsch synthesis of Co-Ru/TiO2-anatase catalysts

A series of Co-Ru/TiO2 catalysts (10wt% Co, 0.5wt% Ru, nominal loadings) were prepared by impregnation of TiO2-anatase supports synthesized with different specific surface areas (Ti-L: 53m2/g, Ti-M: 117m2/g, and Ti-H: 148m2/g) by tuning the conditions of the hydrothermal synthesis and/or the calcination treatments. The most relevant physicochemical properties of supports and catalysts were determined by a set of techniques including ICP-OES, XRD, N2 physisorption, electron microscopy (FESEM, HAADF-STEM, HR-TEM), H2-TPR, H2 chemisorption, and IR-CO. Oxidized precursors were reduced in-reactor under flowing pure H2 at 400°C for 10h and evaluated for Fischer-Tropsch synthesis (FTS) in a fixed bed reactor at 220°C, 2.0MPa, and H2/CO molar ratio of 2. These catalysts exhibited the well-known strong metal-support interaction (SMSI) effect reported for TiO2 materials by which partially reduced TiOx species formed during the catalyst reduction step migrate and decorate the surface of the supported metal phases. The extent to which the SMSI effect occurred was found to increase with the surface area of the TiO2-anatase carrier, as supported by H2 chemisorption, TEM, and IR-CO surface titration experiments. As a consequence, the activity per total mass of cobalt or cobalt-time-yield (CTY) of the Co-Ru/TiO2 catalysts gradually declined with the increase in support surface area: Co-Ru/Ti-L>Co-Ru/Ti-M>Co-Ru/Ti-H. The catalysts, however, displayed similar initial TOFs, implying a negligible influence of the SMSI effect on the initial intrinsic activity of the surface Co0 sites. The high surface area Co-Ru/Ti-H catalyst exhibiting the most pronounced SMSI also presented the lowest C5+ selectivity. This behavior was explained by considering the contribution of two effects: the lower resistance to the intraparticle diffusion of α-olefins when increasing the support surface area, as inferred from the olefin-to-paraffin ratios and the values of the diffusion-related parameter χ, and the reduction in size of the cobalt ensembles on the terraces of Co0 nanoparticles, connected to the extent of SMSI, on which chain growth events are favored.

A homogeneous molecular system for the photogeneration of hydrogen from water based on a [RuII(bpy)3]2+ photosensitizer and a phthalycyanine cobalt catalyst

In this contribution, we report an efficient homogeneous system for the visible light-driven H2 production from aqueous protons. This comprises a macrocyclic phthalycyanine cobalt complex [CoIIPc(-2)] as a hydrogen-evolving catalyst (HEC), [RuII(bpy)3]Cl2 (bpy = 2,2′-bipyridine) as a photosensitizer (PS) and triethylamine (TEA) as a sacrificial electron donor (SED). The system gives up to 2400 TON versus the catalyst with an initial TOF as high as 680 TON h−1. Phthalocyanine cobalt and its derivatives are a promising new direction for molecular catalysts readily accessible in a large scale and low-cost achieving the photogeneration of H2.

Aqueous Biphasic Systems for the Synthesis of Formates by Catalytic CO2 Hydrogenation: Integrated Reaction and Catalyst Separation for CO2 -Scrubbing Solutions.

Aqueous biphasic systems were investigated for the production of formate–amine adducts by metal‐catalyzed CO2 hydrogenation, including typical scrubbing solutions as feedstocks. Different hydrophobic organic solvents and ionic liquids could be employed as the stationary phase for cis‐[Ru(dppm)2Cl2] (dppm=bis‐diphenylphosphinomethane) as prototypical catalyst without any modification or tagging of the complex. The amines were found to partition between the two phases depending on their structure, whereas the formate–amine adducts were nearly quantitatively extracted into the aqueous phase, providing a favorable phase behavior for the envisaged integrated reaction/separation sequence. The solvent pair of methyl isobutyl carbinol (MIBC) and water led to the most practical and productive system and repeated use of the catalyst phase was demonstrated. The highest single batch activity with a TOFav of approximately 35 000 h−1 and an initial TOF of approximately 180 000 h−1 was achieved in the presence of NEt3. Owing to higher stability, the highest productivities were obtained with methyl diethanolamine (Aminosol CST 115) and monoethanolamine (MEA), which are used in commercial scale CO2‐scrubbing processes. Saturated aqueous solutions (CO2 overpressure 5–10 bar) of MEA could be converted into the corresponding formate adducts with average turnover frequencies up to 14×103 h−1 with an overall yield of 70 % based on the amine, corresponding to a total turnover number of 150 000 over eleven recycling experiments. This opens the possibility for integrated approaches to carbon capture and utilization.

High-density defects on PdAg nanowire networks as catalytic hot spots for efficient dehydrogenation of formic acid and reduction of nitrate.

Controlling the surface defects of nanocrystals is a new way of tuning/boosting their catalytic properties. Herein, we report networked PdAg nanowires (NWs) with high-density defects as catalytic hot spots for efficient catalytic dehydrogenation of formic acid (FA) and catalytic reduction of nitrates. The networked PdAg NWs exhibit composition-dependent catalytic activity for the dehydrogenation reaction of FA without any additive, with Pd5Ag5 NWs exhibiting the highest activity. They also show good durability, reflected by the retention of their initial activity during the dehydrogenation reaction of FA even after five cycles. Their initial TOF is 419 h-1 at 60 °C in water solution, much higher than those of the most Pd-based catalysts with a support. Moreover, they can efficiently reduce nitrates to alleviate nitrate pollution in water (conversion yield >99%). This strategy opens up a new green synthetic technique to design support-free heterogeneous catalysts with high-density defects as catalytic hot spots for efficient dehydrogenation catalysis of FA to meet the requirement of fuel cell applications and catalytic reduction of nitrates in water polluted with nitrates.

μ-Pyridine-bridged copper complex with robust proton-reducing ability.

The binuclear copper complex [Cu(DQPD)]2 (where DQPD = deprotonated N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH2)) was synthesised and characterised by various spectroscopic as well as electrochemical techniques. The binuclear copper complex was converted into a mononuclear one by the addition of 2 equivalents of pTsOH into [Cu(DQPD)]2. The interconversion between the dimer and monomer complex was studied through UV-Vis spectroscopy and cyclic voltammetry. The mononuclear copper complex showed high catalytic activity towards electrochemical proton reduction using acetic acid as the external proton source in 95 : 5 (v/v) DMF/H2O. It showed an ic/ip (where ic is the catalytic current in the presence of acetic acid and ip is the reduction peak current in absence of acid) value of 24 and a turnover rate (TOF) of 111.70 s-1 at a scan rate of 100 mV s-1 at 25 °C. The [Cu(DQPD)]2 complex evolved hydrogen under the irradiation of visible light in the presence of fluorescein (Fl) as a photosensitizer and triethylamine (TEA) as the sacrificial electron donor with an initial TOF of 0.03 s-1 with respect to the catalyst.

Influence of acidic properties of different solid acid catalysts for glycerol acetylation

The glycerol esterification with acetic acid is studied in this work using propylsulfonic functionalized mesoporous silica (Pr-SO3H-SBA-15), and compared with H-ZSM-5 and H-Beta zeolites. The reaction was carried out in a batch reactor using a 6:1 molar ratio of acetic acid to glycerol. The initial TOF for the glycerol conversion was significantly higher in the propylsulfonic mesoporous silica, as compared to the two zeolites. These two catalysts have acid sites densities (μmolm−2) that are less than half than that displayed by the SBA-based catalyst. It was possible to obtain 96% conversion in 2.5h, with 87% selectivity to the products of interest diacetylglycerol (DAG) + triacetylglycerol (TAG), being the ratio DAG/TAG=1.7. The catalyst deactivates partly due to sulfonic groups loss and to coke deposition during the reaction, as observed when it was used in a second reaction cycle without any treatment in between cycles. The catalyst lost activity, but maintained the selectivity, associated to a non-selective site poisoning.

Photoactive Metal-Organic Framework and Its Film for Light-Driven Hydrogen Production and Carbon Dioxide Reduction.

The design of a new photocatalytic system and integrating the essential components in a structurally controlled manner to create artificially photosynthetic systems is high desirable. By incorporating a photoactive triphenylamine moiety to assemble a Gd-based metal-organic framework as a heterogeneous photosensitizer, new artificial systems were constructed for the proton and carbon dioxide reduction under irradiation. The assembled MOFs exhibited a one-dimensional metal-oxygen pillar that was connected together by the depronated TCA(3-) ligands to form a three-dimensional noninterpenetrating porous framework. The combining of proton reduction and/or the carbon dioxide reduction catalysts, i.e., the Fe-Fe hydrogenase active site models and the Ni(Cyclam) complexes, initiated a photoinduced single electron transfer from its excited state to the substrate. The system exhibited an initial TOF of 320 h(-1) of hydrogen per catalyst and an overall quantum yield of about 0.21% and is able to reduce carbon dioxide under irradiation. The deposit of the photoactive Gd-TCA into the film of an α-Al2O3 plate provided a platform for the practical applications through prolonging the lifetime of the artifical system and allowed the easily operated devices being recyclable as a promising photocatalytic system.

Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

The effect of calixarene ligand symmetry, as dictated by lower-rim substitution pattern, on the coordination to a Ti(IV) cation is assessed in solution and when grafted on SiO2, and its effect on epoxidation catalysis by Ti(IV)-calixarene grafted on SiO2 is investigated. C2v symmetric Ti-tert-butylcalix[4]arene complexes that are 1,3-alkyl disubstituted at the lower rim (di-R-Ti) are compared to previously reported grafted Cs symmetric complexes, which are singly substituted at the lower rim (mono-R-Ti). 13C MAS NMR spectra of complexes isotopically enriched at the lower-rim alkyl position indicate that di-R-Ti predominantly grafts onto silica as the conformation found in solution, exhibiting a deshielded alkyl resonance compared to the grafted mono-R-Ti complexes, which is consistent with stronger alkyl ether→Ti dative interactions that are hypothesized to result in higher electron density at the Ti center. Moreover, 13C MAS NMR spectroscopy detects an additional contribution from an “endo” conformer for grafted di-R-Ti sites, which is not observed in solution. Based on prior molecular modeling studies and on 13C MAS NMR spectroscopy chemical shifts, this “endo” conformer is proposed to have similar Ti–(alkyl ether) distances at the lower-rim and electron density at the Ti center relative to grafted mono-R-Ti complexes. Differences between grafted mono-R-Ti and di-R-Ti sites can be observed by ligand-to-metal charge transfer edge-energies, calculated from diffuse-reflectance UV–visible spectroscopy at 2.24 ± 0.02 and 2.16 ± 0.02 eV, respectively. However, rates of tert-butyl hydroperoxide consumption in the epoxidation of 1-octene are found to be largely unchanged when compared to those of the grafted mono-R-Ti complexes, with average rate constants of ~1.5 M−2 s−1 and initial TOF of ~4 ks−1 at 323 K. This suggests that an “endo” conformation of grafted di-R-Ti may prevail during catalysis. Despite this, grafted di-C1-Ti complexes can be more selective than mono-C1-Ti complexes (45 vs. 34 % at a 50 % conversion at 338 and 353 K), illustrating the importance of the Ti coordination environment on epoxidation catalysis.