Indium Catalyst Research Articles

3D hierarchical porous indium catalyst for highly efficient electroreduction of CO2

A highly porous indium electrode was prepared with a facile electrodeposition method, which delivers remarkable activity and selectivity towards electro reduction of Co2.

Effect of indium catalyst particle size on the morphology of silicon oxide nanowires

Silicon oxide (SiOx, × ≤2) nanowires were synthesized on indium (In) catalyst particles by gas-jet electron beam plasma-enhanced chemical vapor deposition through the vapor-liquid-solid (VLS) mechanism. The synthesis was carried out on substrates of different average particle sizes in the range from 42 to 710 nm. Arrays of oriented microropes of nanowires were grown on catalysts with a particle size of 42 and 79 nm. On 170 nm catalyst particles, cocoon-like structures from nanowires were formed, and on 710 nm particles, the synthesis proceeded in the same way as on an indium tin oxide (ITO) film. The chemical composition of the synthesized nanostructures was studied by Fourier transform infrared spectroscopy. Under the assumption of a uniform distribution of silicon and oxygen atoms, the nanowires were found to consist of SiOx with x = 1.9. Energy dispersive spectroscopy showed that the catalyst particles consisted of non-stoichiometric indium oxide, rather than of pure indium. Therefore, during the synthesis of silicon oxide nanowires on an indium catalyst, hydrogen should be used.

Cyclohepta[ b]indole Synthesis through [5 + 2] Cycloaddition: Bifunctional Indium(III)-Catalyzed Stereoselective Construction of 7-Membered Ring Fused Indoles.

A new approach for the synthesis of highly functionalized tetrahydrocyclohepta[ b]indoles through [5 + 2] cycloaddition was developed. Two carbon-carbon bonds were formed by the simple addition of an indium catalyst, which acted as both a π-Lewis acid and σ-Lewis acid to activate the alkyne and unsaturated ester, respectively. The reaction could be applied to various substrates and proceeded regio- and diastereoselectively in all cases.

Indium-Catalyzed Direct Conversion of Lactones into Thiolactones Using a Disilathiane as a Sulfur Source.

An indium-catalyzed reaction of lactones and a disilathiane leading to thiolactones is described. The direct synthesis of thiolactones from lactones with an appropriate sulfur source is one of the most attractive approaches in organic and pharmaceutical chemistry. In this context, we found an indium-catalyzed direct conversion of lactones into thiolactones in the presence of elemental sulfur and a hydrosilane via formation of the disilathiane in situ. On the basis of the previous reaction, the application utilizing the disilathiane as a sulfur source was performed herein for the efficient synthesis of a variety of thiolactone derivatives from lactones by an indium catalyst.

Coupling of Epoxides and Lactones by Cationic Indium Catalysts To Form Functionalized Spiro‐Orthoesters

AbstractWe prepared a cationic indium catalyst for the conversion of epoxides and lactones into spiro‐orthoesters (SOEs), a family of expanding monomers. The cationic indium alkyl complexes [(NNiO)In(CH2SiMe3)(S)][B{3,5‐(CF3)2C6H3}4] (2⋅Solv; H(NNiO)=2,4‐dicumyl‐6‐({[2‐(dimethylamino)cyclohexyl]imino}methyl)phenol, S=OEt2 or THF) were synthesized and fully characterized. The reaction of ϵ‐caprolactone with 1,2‐epoxy‐7‐octene resulted in the formation of 2‐(hex‐5‐en‐1‐yl)‐1,4,6‐trioxaspiro[4.6]undecane (SOE1) with full conversion of both components. We extended the substrate scope to five‐ and six‐membered lactones as well as to a number of functionalized epoxides. The reactivity of the SOEs was explored.

Indium Catalysts for Low-Pressure CO2/Epoxide Ring-Opening Copolymerization: Evidence for a Mononuclear Mechanism?

The alternating copolymerization of CO2/epoxides is a useful means to incorporate high levels of carbon dioxide into polymers. The reaction is generally proposed to occur by bimetallic or bicomponent pathways. Here, the first indium catalysts are presented, which are proposed to operate by a distinct mononuclear pathway. The most active and selective catalysts are phosphasalen complexes, which feature ligands comprising two iminophosphoranes linked to sterically hindered ortho-phenolates. The catalysts are active at 1 bar pressure of carbon dioxide and are most effective without any cocatalyst. They show low-pressure activity (1 bar pressure) and yield polymer with high carbonate linkage selectivity (>99%) and isoselectivity ( Pm > 70%). Using these complexes, it is also possible to isolate and characterize key catalytic intermediates, including the propagating indium alkoxide and carbonate complexes that are rarely studied. The catalysts are mononuclear under polymerization conditions, and the key intermediates show different coordination geometries: the alkoxide complex is pentacoordinate, while the carbonate is hexacoordinate. Kinetic analyses reveal a first-order dependence on catalyst concentration and are zero-order in carbon dioxide pressure; these findings together with in situ spectroscopic studies underpin the mononuclear pathway. More generally, this research highlights the future opportunity for other homogeneous catalysts, featuring larger ionic radius metals and new ligands, to operate by mononuclear mechanisms.

Selective and Stable Electroreduction of CO2 to CO at the Copper/Indium Interface

Electrochemical reduction of CO2 using renewable energy is a promising strategy to mitigate the CO2 emissions and to produce valuable chemicals. However, the lack of highly selective, highly durable, and nonprecious-metal catalysts impedes the applications of this reaction. In this work, copper-nanowire-supported indium catalysts are proposed as advanced electrocatalysts for the aqueous electroreduction of CO2. The catalysts are synthesized by a facile method, which combines In3+ deposition on Cu(OH)2 nanowires, mild oxidation, and in situ electroreduction procedures. With a thin layer of metallic In deposited on the surface of the Cu nanowires, the catalyst exhibits a CO Faradaic efficiency of ∼93% at −0.6 to −0.8 V vs RHE; additionally, an unprecedented stability of 60 h is achieved. The characterization results combined with density functional theory (DFT) calculations reveal that the interface of Cu and In plays an essential role in determining the reaction pathway. The calculation results suggest tha...

Indium‐Assisted Plasma‐Enhanced Low‐Temperature Growth of Silicon Oxide Nanowires

The nanowires of the silicon oxide SiOx (x ≤ 2) are synthesized on an indium catalyst by the gas‐jet electron beam plasma chemical vapor deposition (GJ EBP CVD) method using a monosilane‐argon‐hydrogen mixture with the simultaneous supply of the oxygen into the vacuum chamber. The arrays of the aligned microropes (bundles) of nanowires are formed at the substrate temperatures of 200–335 °С. At the temperature of 160 °С the cocoon‐like structures of SiOx nanowires are synthesized. The obtained results are explained within the synthesis model suggested previously. The Fourier transform infrared (FTIR) transmittance spectra are recorded to study the chemical composition of the nanowires. It is shown that the nanowires synthesized at temperatures of 200–335 °С consist of SiOx with x = 1.93 ± 0.04. The arrays of the oriented microropes of the SiOx nanowires exhibit the intense photoluminescence at a room temperature with a maximum in a range of the energies from 2 to 3 eV. The photoluminescence spectra of the oriented microropes synthesized on silicon substrates with the indium catalyst are shifted toward lower energies from 2.7–2.8 to 2.4–2.5 eV at the changing growth temperatures from 200 to 335 °C.

Surface Species and Metal Oxidation State during H2-Assisted NH3-SCR of NOx over Alumina-Supported Silver and Indium

Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NOx with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy was used to follow the oxidation state of the silver and indium phases, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to elucidate the formation of surface species during SCR conditions. In addition, the NOx reduction efficiency of the materials was evaluated using H2-assisted NH3-SCR. The DRIFTS results show that the Ag/Al2O3 sample forms NO-containing surface species during SCR conditions to a higher extent compared to the In/Al2O3 sample. The silver sample also appears to be more reduced by H2 than the indium sample, as revealed by UV-vis spectroscopic experiments. Addition of H2, however, may promote the formation of highly dispersed In2O3 clusters, which previously have been suggested to be important for the SCR reaction. The affinity to adsorb NH3 is confirmed by both temperature programmed desorption (NH3-TPD) and in situ DRIFTS to be higher for the In/Al2O3 sample compared to Ag/Al2O3. The strong adsorption of NH3 may inhibit (self-poison) the NH3 activation, thereby hindering further reaction over this catalyst, which is also shown by the lower SCR activity compared to Ag/Al2O3.

Aromatic interactions in aryl-capped polylactides: A thermorheological investigation

A series of aryl-capped poly(lactide)s (PLAs) were synthesized by living ring-opening polymerization with a chain transfer agent (also referred to as immortal polymerization, iROP) using a previously reported dinuclear indium catalyst, [(NNO)InCl]2(μ-Cl)(μ-OEt) (A). For understanding the extent and strength of association caused by the arylated chain ends, end-functionalized PLAs were analysed using thermal, rheological, and mechanical techniques. We show that the end-group has a greater effect on the properties of low molecular weight PLAs due to the larger number density of the aryl end groups; significant interactions can be induced under oscillatory shear conditions in the low frequency flow regime (terminal zone). The effects of associations on the extensional properties are also discussed.

Indium Catalysts for Ring Opening Polymerization: Exploring the Importance of Catalyst Aggregation.

Inexorably, the environmental persistence and damage caused by polyolefins have become major drawbacks to their continued long-term use. Global shifts in thinking from fossil-fuel to renewable biobased resources have urged researchers to focus their attention on substituting fossil-fuel based polymers with renewable and biodegradable alternatives on an industrial scale. The recent development of biodegradable polyesters from ring opening polymerization (ROP) of bioderived cyclic ester monomers has emerged as a promising new avenue toward this goal. Ever increasing numbers of metal-based initiators have been reported in the literature for the controlled ROP of cyclic esters, in particular for the polymerization of lactide to produce poly(lactic acid) (PLA). PLA has several material weaknesses, which hinder its use as a replacement for commodity plastics. Despite many advances in developing highly active and controlled catalysts for lactide polymerization, no single catalyst system has emerged to replace industrially used catalysts and provide access to PLA materials with improved properties. We reported the first example of indium(III) for the ring opening polymerization of lactide. Since then, indium(III) has emerged as a useful Lewis acid in initiators for the controlled polymerization of lactide and other cyclic esters. In particular, we have developed a large family of chiral dinuclear indium complexes bearing tridentate diaminophenolate ligands and tetradentate salen and salan ligands. Complexes within our tridentate ligand family are highly active initiators for the moderately isoselective living and immortal polymerization of rac-lactide, as well as other cyclic esters. We have shown that subtle steric effects influence aggregation in these systems, with polymerization typically proceeding through a dinuclear propagating species. In addition, profound effects on polymerization activities have been observed for central tertiary versus secondary amine donors in these and other related systems. In contrast, our well-controlled and highly active chiral indium salen systems are more isoselective than the tridentate analogues and polymerize lactide via a mononuclear propagating species. Again, we have noticed that subtle steric and electronic changes to the ligand can influence both polymerization activity and stereoselectivity via aggregation phenomena. Recently, we have reported a promising new chiral indium catalyst supported by a tetradentate salan ligand. This catalyst is remarkably water and air stable and can be activated by linear and branched alcohols to provide controlled access to multiblock copolymers in air. This catalyst represents an important step forward toward generating new, commercially relevant catalysts for ROP of cyclic esters to produce novel biodegradable polymers, and highlights the unique value of indium-based catalysts in the field.

Air- and Moisture-Stable Indium Salan Catalysts for Living Multiblock PLA Formation in Air

We introduce an air- and moisture-stable hydroxy-bridged indium salan complex as a highly active and controlled catalyst for the ring-opening polymerization of cyclic esters in air. The reversible activation of this complex with linear and branched alcohols leads to immortal polymerization, allowing the controlled formation of block copolymers in air. It is the only reported example of a living catalyst that remains controlled after multiple exposures to ambient air at high temperatures. Although the prevalent catalyst for ring-opening polymerization, tin octanoate, is robust, it does not promote controlled polymerization. Our indium catalyst is exceptional in being both robust and controlled.

Highly efficient In–Sn alloy catalysts for electrochemical reduction of CO2 to formate

Gas diffusion electrodes (GDEs), including GDE-In0.90Sn0.10, GDE-In0.47Sn0.53 and GDE-In0.22Sn0.78, were prepared by electrodeposition of In–Sn alloys on carbon fiber paper, and then used to explore the electroreduction of CO2 to formate in aqueous solution. Compared with commercial indium or Sn foil catalysts, the GDE-In0.90Sn0.10 electrode in particular is shown to have excellent catalytic performance towards electroreduction of CO2 to formate, with a high Faradaic efficiency (~92%). More importantly, the catalytic activity of GDE-In0.90Sn0.10 remained reasonably stable over a 22-hour period of electrolysis, and a relatively high electrolytic current density (15mAcm−2) was obtained in an aqueous medium, demonstrating its potential for electrochemical reduction of CO2 to formate.

Self-catalyst assisted and catalyst-free epitaxial growth of InAs on Ge (111): Role of substrate surface and evolution of polytypism

In the present work, the authors report on the role of a self-catalyst (indium) and a substrate surface in various growth mechanisms and the crystalline structure of InAs nucleating layers on Ge (111) using metal organic vapor phase epitaxy. This study opens up the possibility of direct integration of InAs with Ge (111) substrates for next generation optoelectronic and microelectronic device applications. Different nucleation modes like droplet-epitaxy (DE), Volmer–Weber (VW), and Frank–Van der Merwe (FM) modes are observed in various growth windows. DE and FM modes are the dominating nucleation modes at lower growth temperature (400–470 °C) with the assistance of indium catalysts, while the VW mode dominates at higher growth temperature (470–540 °C). Three dimensional faceted structures are formed with varying densities in the overall growth temperature range of 400–540 °C, which is attributed to various factors like surface strain of the indium adatom covered Ge (111) surface, indium surface diffusion, and twin defect formation. High resolution x-ray diffraction identifies the twin formation at low growth temperature. Raman mapping reveals that InAs nano-/microstructures grow with a zinc blende-wurtzite polytypic crystal structure at higher growth temperature and arsenic-rich conditions. A comparison is made on the growth modes, morphology, and polytypism in InAs nanostructures, which are grown on Ge (111) and Si (111) substrates under identical conditions. Low surface diffusivity of indium on the Ge substrate and InAs/Ge interface energy are proposed as the main factors for the inhibition of anisotropic axial growth of InAs on Ge via the vapor-liquid-solid mode, while they succeed on the Si substrate.

Liquid‐Metal Indium Catalysis for Direct Dehydrogenative Conversion of Methane to Higher Hydrocarbons

AbstractCatalysts for dehydrogenative conversion of methane (DCM) to higher hydrocarbons are worthy of attention. Indium supported on silica (In/SiO2) was found for effective catalyst for the DCM reaction above 1023 K. Products were ethane, ethylene, acetylene, propylene, benzene, toluene, naphthalene and hydrogen. A highest selectivity of sum of products was 96 % at 1098 K and a steady‐state sum yield was 2.1 % with 63 % selectivity at 1173 K. Characterization studies using temperature‐programed X‐ray diffraction (TP‐XRD) and scanning electron microscopy (SEM) indicated that the working state of indium catalyst was liquid metal. Effects of reaction temperature on the product distribution and studies of temperature‐programed‐reaction (TPR) indicated that liquid‐metal indium activated methane and selectively converted to ethane. Higher hydrocarbons were produced from ethane in the gas phase without catalyst.

Catalytic Nitrate Removal in a Trickle Bed Reactor: Direct Drinking Water Treatment

Palladium (Pd)‐based catalysts hold promise as an alternative water treatment technology for nitrate (NO3), but practical application requires a flow‐through reactor that efficiently delivers hydrogen (H2) from gas to water. A trickle bed reactor (TBR) packed with a 0.1 percent by weight (wt%) Pd–0.01 wt% In/γ‐Al2O3 (indium and porous aluminum oxide) catalyst was evaluated to address this challenge. Catalytic activity generally increased with H2 superficial velocity (0.65–29.6 m/h) and liquid (deionized water) superficial velocities from 14.8 to 26.6 m/h before decreasing at 38.5 m/h. This decrease corresponded to a change in flow regime and suggests that optimal TBR performance occurs at the transition from pulse to bubble flow. An optimal TBR activity of 19.5 ± 1.3 mg NO3/min‐g Pd was obtained; this is only ~18% of the batch reactor activity as a result of H2 mass transfer limitations, but three to 15 times greater than activities obtained with previous flow‐through reactors. Catalyst deactivation occurred in the TBR after 41 days of operation, motivating the need for improved fouling mitigation strategies.

Catalytic Denitrification in a Trickle Bed Reactor: Ion Exchange Waste Brine Treatment

Catalytic reduction of nitrate in ion exchange (IX) waste brine for reuse is a promising option for reducing IX costs and environmental impacts. A recycling trickle bed reactor (TBR) was designed and optimized using 0.5 percent by weight (wt%) palladium–0.05 wt% indium catalysts supported on US mesh size 12 × 14 or 12 × 30 activated carbon particles. Various liquid superficial velocities (Ur) and hydrogen gas superficial velocities (Ug‐H2) were evaluated to assess performance in different flow regimes; catalyst activity increased with Ug‐H2 at all Ur for both catalysts and was greatest for the 12 × 30 catalyst at the lowest Ur (8.9 m/h). The 12 × 30 catalyst demonstrated up to 100% higher catalytic activity and 280% higher mass transfer rate compared with the 12 × 14 catalyst. Optimal TBR performance was achieved with both catalysts in the trickle flow regime. The results indicate that the TBR is a promising step forward, and continued improvements are possible to overcome remaining mass transfer limitations.

Phosphasalen Indium Complexes Showing High Rates and Isoselectivities in rac-Lactide Polymerizations.

Polylactide (PLA) is the leading bioderived polymer produced commercially by the metal‐catalyzed ring‐opening polymerization of lactide. Control over tacticity to produce stereoblock PLA, from rac‐lactide improves thermal properties but is an outstanding challenge. Here, phosphasalen indium catalysts feature high rates (30±3 m −1 min−1, THF, 298 K), high control, low loadings (0.2 mol %), and isoselectivity (P i=0.92, THF, 258 K). Furthermore, the phosphasalen indium catalysts do not require any chiral additives.

Phosphasalen Indium Complexes Showing High Rates and Isoselectivities in rac‐Lactide Polymerizations

AbstractPolylactide (PLA) is the leading bioderived polymer produced commercially by the metal‐catalyzed ring‐opening polymerization of lactide. Control over tacticity to produce stereoblock PLA, from rac‐lactide improves thermal properties but is an outstanding challenge. Here, phosphasalen indium catalysts feature high rates (30±3 m−1 min−1, THF, 298 K), high control, low loadings (0.2 mol %), and isoselectivity (Pi=0.92, THF, 258 K). Furthermore, the phosphasalen indium catalysts do not require any chiral additives.

Indium-Catalyzed Reductive Dithioacetalization of Carboxylic Acids with Dithiols: Scope, Limitations, and Application to Oxidative Desulfurization.

In this study an InI3-TMDS (1,1,3,3-tetramethyldisiloxane) reducing system effectively catalyzed the reductive dithioacetalization of a variety of aromatic and aliphatic carboxylic acids with 1,2-ethanedithiol or 1,3-propanedithiol leading to the one-pot preparation of either 1,3-dithiolane derivatives or a 1,3-dithiane derivative. Also, the intact indium catalyst continuously catalyzed the subsequent oxidative desulfurization of an in situ formed 1,3-dithiolane derivative, which led to the preparation of the corresponding aldehydes.