The La based perovskite type LaMO3 (M = Ni, Co) oxides were prepared by combustion synthesis method using citric acid as organic fuel. These catalyst precursors tested for ammonia decomposition. The LaNiO3 and LaCoO3 catalysts showed good activity for NH3 decomposition. The LaNiO3 catalyst displayed greater activity than LaCoO3. This due to high surface area and easily reducibility of Ni species. A 50% of La was substituted by Ce in both LaNiO3 and LaCoO3 catalysts. A remarkable effect on catalytic performance was observed with the partial substitution of La by Ce in perovskite catalyst especially at lower temperatures. The La0.5Ce0.5NiO3 catalyst exhibited highest activity among all prepared samples. The achieved superior activity is due to boost in surface area, reducibility and suitable basicity. The SEM elemental mapping of La0.5Ce0.5NiO3 catalyst concluded that metal oxide constituents dispersed homogeneously. The La0.5Ce0.5NiO3 catalyst showed excellent stable catalytic performance during 50 h time on study at 550 °C.

Mesoporous tantalum-zirconium oxide (TZ) solid acid catalysts were synthesized by sol-gel method and employed in the biodiesel production from higher water (2.0 and 4.0 wt%) and palmitic acid (20.0 wt%) added soybean oil (SBO) or yellow grease feedstocks. Characterization of TZ catalysts were done by using BET-surface area, XRD, Raman spectroscopy, XPS and NH3-TPD techniques. Only 35.0% methyl palmitate and 14.0% SBO fatty acid methyl ester (FAME) yield was obtained on bare ZrO2 at 180 degrees C. Addition of tantalum to ZrO2 significantly improved the yield of methyl palmitate (95.0%) and SBO FAME (88.6%) at 180 degrees C. The greater ester yield on TZ catalysts was associated with improved acidity due to the presence of Ta-O-Ta, Ta--O and Zr-O-Ta species which readily interacted with methanol and triglycerides. Further, 20.0 mol.% tantalum loaded zirconium oxide catalyst (20TZ) exhibited consistent biodiesel yield upto two recycles of feed containing 2.0 wt% of added water and 20 wt% PA in SBO. It is noteworthy that, 80.0% yellow grease FAME formation was observed on 20TZ catalyst at 180 degrees C. The results emphasize, TZ solid acid catalysts are highly efficient compared to polyoxometalates and or sulphated zirconium oxide solid acid catalysts for biodiesel production from higher water and free fatty acid containing feedstocks.

The first SuFEx click chemistry synthesis of SOF4-derived copolymers based upon the polymerization of bis(iminosulfur oxydifluorides) and bis(aryl silyl ethers) is described. This novel class of SuFEx polymer presents two key characteristics: First, the newly created [-N=S(=O)F-O-] polymer backbone linkages are themselves SuFExable and primed to undergo further high-yielding and precise SuFEx-based post-modification with phenols or amines to yield branched functional polymers. Second, studies of individual polymer chains of several of these new materials indicate the presence of helical polymer structures, which itself suggests a preferential approach of new monomers onto the growing polymer chain upon the formation of the stereogenic linking moiety.

The aim of this work is to understand the influence of second metals (M = Ce or Pd or Nb) on Mo2C active phase reduction into metallic molybdenum and on surface MoOx species of M-Mo2C/HZSM-5 catalysts studied for methane dehydroaromatization at 700 °C with GHSV 1800 mL. gcat−1. h−1. The fresh and spent catalysts were characterized by using ATR-FTIR, HRTEM/STEM, BET surface area, XRD, TPO, NH3-TPD-mass, XPS and H2-TPR techniques. Essentially, the highest benzene yield of 8.4% on Pd–Mo2C/HZSM-5 catalyst for 10 h of continuous operation was associated with limited Mo2C active phase reduction into metallic molybdenum at Pd–Mo proximity via Pd2+ to Pd0 step and promoted coke burning through reduced carbon deposits formation. Further, the surface reduction of CeO2 to Ce2O3 decreased the methane conversion due to sluggish MoOx species transformation to Mo2C active phase. On the other side, Nb2O5 primarily reduced into NbO2/NbO resulted in surface MoOx species and external surface Mo2C particles eventually produced superior coke via CH4 decomposition on Nb–Mo2C/HZSM-5 catalyst. The decreasing order of benzene yield after 10 h of reaction at 700 °C as follows: Pd–Mo2C/HZSM-5 (8.4%) > Mo2C/HZSM-5 (7.4%) > Nb–Mo2C/HZSM-5 (5.8%) > Ce–Mo2C/HZSM-5 (5.2%).

Excellent CO2 hydrogenation activity results were obtained on Cu-Zn-Al-K (CZA-K) catalyst with 10% of CO2 conversion and 98% of methanol selectivity at 220 degrees C. The CZA-K catalyst was precipitated by using 4 M K2CO3/KOH solution. For comparison purpose, CZA-Na and CZA catalysts were synthesized by using 4 M solutions of Na2CO3/NaOH and (NH4)(2)CO3/NH4OH respectively. Characterization of these catalysts was done by using BET-poresize, XRD, FTIR-DRIFTs, high pressure-TPR, CO2-TPD-mass, XPS and HAADF-STEM-EDX techniques. Among the catalysts studied maximum methanol space time yield of 14.4 mmol.g(cat)(-).h(-) was obtained on CZA-K at 240 degrees C with 2400 h(-) GHSV of CO2/H-2 mole ratio equals to 1:4. Greater methanol yield was associated with superior surface Cu+/Cu-0 content in CZA-K was obtained through K2CO3/ KOH precipitation. Further, FTIR-DRIFTs spectra suggests the interaction of CO(2 )with the potassium existed in the CZA framework (0.65% K, EDX) led to the formation of K-O-(CO)-O surface species. To some extent, CO2 dissociation to CO and subsequent CH4 formation was limited by this species in presence of H-2. At 240 degrees C, steady catalytic activity was observed for 100 h of continuous operation on CZA-K. It was associated with fewer carbon deposits formation and segregated active metals in CZA-K catalyst. The decreasing order of CO2 hydrogenation activity at 240 degrees C with 3.0 MPa feed-gas pressure as follows: CZA-K (14% CO2 conversion and 96% methanol selectivity) > CZA-Na (11% and 94%) > CZA (9% and 92%). (C) 2020 The Authors. Published by Elsevier B.V. on behalf of King Saud University.

High surface area tungsten nitride catalysts synthesized from ammonium meta-tungstate and employed as catalysts for ecofriendly H-2 production from NH3. A series of tungsten nitride catalysts synthesized by using CiA (citric acid) as chelating agent with different molar ratio of W and CiA. The synthesized materials characterized using BET-surface area, X-ray diffraction, X-ray photoelectron spectroscopy and SEM techniques. The BET value of as-synthesized tungsten nitride was raised from 25 to 80 m(2) g(-1). The influence of amount of CiA in preparation on the catalysts surface area was investigated. The catalyst performance measured within the desired range of temperature 300-600 degrees C. A pure phase of tungsten nitride was formed by this preparation method. The catalyst with the ratio of CiA/W = 3 exhibited the best catalytic performance. The increased activity of WN-31 catalyst was mainly due to increased surface area, decreased particle size and high surface concentration. The WN-31 catalyst showed stable performance during time on study for 25 h. These bulk tungsten-based materials are easy to synthesize and highly stable material in the reaction atmosphere. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Here in, for the first time we are reporting molybdenum carbide reduction into metallic molybdenum during methane aromatization on HZSM-5 (Si/Al ratio = 23, 30, 50 and 80) at methane space velocity of 1800 mL.gcat−.h−. Benzene yield was influenced by the surface metallic molybdenum through the non-aromatic carbon deposits formation via linear hydrocarbons degradation on HZSM-5 with fewer acidity (Si/Al ratio = 30, 50 and 80). Our XPS analysis results demonstrated improved surface metallic molybdenum in spent Mo2C/HZSM-5 = 80 (0.71 atom. %) and 50 (0.54 atom. %) samples over Mo2C/HZSM-5 = 30 (0.33 atom. %) and 23 (0.20 atom. %) samples. Furthermore, HR-TEM and FFT analysis images clearly established fine distribution of distorted spherical shaped Mo2C particles with 6–14 nm size in spent Mo2C/HZSM-5 = 23. On the other hand, Mo2C particle size was increased upto 22 nm in Mo2C/HZSM-5 = 80. The ease reduction of Mo2C into metallic molybdenum and aggregation of Mo2C particles in spent higher Si to Al ratio (50 and 80) samples was associated with weak interactions between Mo2C and the HZSM-5 with fewer acidity. At 700 °C, the order of benzene yield as follows: Mo2C/HZSM-5 = 80 (2.2%) < Mo2C/HZSM-5 = 50 (3.25%) < Mo2C/HZSM-5 = 30 (5.2%) < Mo2C/HZSM-5 = 23 (8.0%).

Silicon nanoparticles (Si NPs) are a good alternative to conventional heavy metal-containing quantum dots in many applications, due to their low toxicity, low cost, and the high natural abundance of the starting material. Recently, much synthetic progress has been made, and crystalline Si NPs can now be prepared in a matter of hours. However, the passivation of these particles is still a time-consuming and difficult process, usually requiring high temperatures and/or harsh reaction conditions. In this paper, we report an easy method for the room-temperature functionalization of hydrogen-terminated Si NPs. Using silanol compounds, a range of functionalized Si NPs could be produced in only 1 h reaction time at room temperature. The coated NPs were fully characterized to determine the efficiency of binding and the effects of coating on the optical properties of the NPs. It was found that Si NPs were effectively functionalized, and that coated NPs could be extracted from the reaction mixture in a straightforward manner. The silanol coating increases the quantum yield of fluorescence, decreases the spectral width and causes a small (∼50 nm) blue-shift in both the excitation and emission spectra of the Si NPs, compared to unfunctionalized particles.

PdZn-based catalysts have evolved as a very effective catalytic material for CO2 hydrogenation to methanol. ZrO2-supported PdZn and Ca-PdZn catalysts, synthesized by the simple impregnation method, exhibited excellent catalytic activity with impressive selectivity to methanol when tested for direct CO2 hydrogenation reaction. These catalysts were able to achieve up to 97-100 % methanol selectivity with significant CO2 conversion (single-pass of more than 10% in the case of Ca-doped PdZn/ZrO2) under reaction conditions of 20-30 bar, 2400 mL/g-h, H-2/CO2 = 3:1, 220-270 degrees C. Addition of calcium to PdZn/ZrO2 catalyst had a positive impact on overall catalytic performance and catalyst lifetime. Ca-doped PdZn/ZrO2 catalyst also showed high stability for at least 100 h (on stream) implying the catalyst was very stable and resistant to sintering. The catalysts were characterized using BET, CO-chemisorption, CO2-TPD, XRD, XPS, SEM-EDS and TPR. Whereas, in-situ DRIFT study identified surface reaction transient intermediates, formates and methoxy species, and therefore, a reaction mechanism of formate pathway is proposed based on the DRIFT analysis.

Mg-Fe Layered Double Hydroxide (LDH) with M2+: M3+ 3:1 stoichiometric ratio was synthesized and employed as catalyst precursor for COx-free hydrogen production from ammonia. The resulting catalyst showed good catalytic activity. A series of Mg/Co-Fe layered double hydroxides were synthesized by replacing Me2+ with Co2+ without disturbing M2+:M3+ ratio. The influence of nature and extent of Co(II) substitution on structure, morphology and surface properties were studied. A systematic study was carried out using these materials as catalyst precursors for ammonia decomposition. BET, XRD, TPR, XPS, CO2-TPD and TEM techniques were used to characterize the synthesized catalysts. These Fe-based catalysts are highly active, highly stable and not promoting any stable surface nitridation during the ammonia decomposition reaction. Among all catalysts, the Mg3Co3Fe2 catalyst showed the highest activity i.e. 100% conversion at 6,000 h(-1) and 60% at 50,000 h(-1) space velocities at 550 degrees C. The registered superior catalytic activity was result of the formed specific catalyst's properties like high surface area, high surface Co and Fe atomic concentration and suitable basicity. These Fe-based materials are, cost-effective, easily synthesize and highly stable, thus attractive for large-scale operation. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Different mole ratio Al-B catalysts (Al-10B to Al-35B) were synthesized by using sol-gel (SG) method. Ethyl benzene (EB) dehydrogenation in the presence of oxygen and water steam was carried out on these catalysts at 450–500 °C with EB contact time of 0.54 gcat.s.cm–3. Acidity of Al-B catalysts was estimated by using NH3-TPD-mass spectral analysis studies. SEM-mapping images revealed fine distribution of boron up to 15% of its loading in alumina (Al-15B), whereas, boron aggregation was observed in higher boron content (Al-25B and Al-35B) catalysts. Essentially, acid sites of very weak strength (Tmax ≤ 125 °C) were observed for Al and Al-10B catalysts and resulted in low EB conversion and styrene yield. On the other hand, acid sites of weak strength (Tmax ≤ 180 °C) were observed for Al-25B and Al-35B catalysts and resulted in high EB conversion. However, greater styrene yield (43.2%) with reasonable EB conversion (46%) was obtained on acid sites of weak moderate strength in Al-15B catalyst. Further, Al-15B catalyst was synthesized by using co-precipitation (COP) and impregnation (IMP) methods. Acid sites related to NOx formation during the NH3-TPD-mass analysis on IMP and COP catalyst essentially improved the EB conversion to 66% and 63% respectively at 500 °C. However, these acid sites were diminished in Al-B SG catalyst and resulted in 50% of EB conversion at 500 °C. At 50% of EB conversion level, styrene selectivity of 73%, 82.5% and 84% were observed on Al-B IMP, Al-B COP and Al-SG catalysts, respectively. Hence, different method of preparation of Al-B catalyst generated acid sites of different strength and density and thereby influenced the styrene formation.

Small sized high quantum yield copper doped CdSe quantum dots (QDs) were prepared by colloidal precipitation method with a high ratio of thiol groups coordinated at the surface of quantum dots. Both of states of Cu oxidation (+1 and +2) were detected for doped quantum dots. The high percentage of +2 oxidation state of Cu ions has been detected in the samples doped with low concentrations, relative to the samples doped with high concentrations of Cu. The optical transition energy of Cu doped CdSe quantum dots decreased relative to undoped dots due to the formation of mid-gap levels. Band edge and surface state emissions have been observed for undoped quantum dots; whereas for Cu doped CdSe, only broad emission band with a large Stokes shift was observed. High quantum yield reaches 63%, as observed for doped structures with low concentrations due to mid-gap level occupying a permanent hole. The quantum dots doped with high concentrations showed a low quantum yield relative to the samples doped with low concentrations. This has resulted due to the competition of hole trapping between Cu1+ state and hole trap species on the surface of quantum confined structures. It was expected to obtain quantum confined structures doped with low concentrations with promising applications in various optoelectronic devices due to high quantum yield and large Stokes shift.

We report the compositional optimization of Pd:Zn/CeO2 catalysts prepared via sol-gel chelatization for the hydrogenation of CO2 under mild reaction conditions. The formation of a PdZn alloy, which is the main active phase for this reaction, was maximized for the catalyst with a Pd to Zn ratio close to 1. For this catalyst, a maximum conversion of 14%, close to thermodynamic equilibrium, and high selectivity to methanol (95%) were achieved at 220 degrees C, 20 bar, 2400 h(-1) GHSV and H-2:CO2 stoichiometric ratio of 3:1. The formation of PdZn alloys was achieved by reducing the catalyst precursor at 550 degrees C under hydrogen flow and confirmed by XRD. XPS study confirmed the presence of Pd, being maximum for the optimized catalyst composition. At lower temperature, i.e. 180 degrees C, 1.0PdZn catalyst showed 100% selectivity to methanol with 8% CO2 conversion. RWGS reaction is responsible for the production of CO and its selectivity increases with temperature. In situ DRIFTS suggests that CO2 is activated as adsorbed CO3- species over CeO2. Surface micro-kinetics demonstrates that methanol can be formed either via formaldehyde or formic acid surface intermediates.

Silver catalysts supported on ceria-zirconia (CZ) mechanically mixed oxide were synthesized by wet impregnation and chelating methods. Nominal loadings of 5 wt.% of Ag was deposited on the CZ support. These catalysts were tested for the CO2 hydrogenation reaction to methanol with feed gas composition of CO2–H2 = 3:1 at 250 °C, 20 bar total pressure and GHSV of 1800 h−1. The calcined and reduced catalysts were characterized using XRD, BET, TPR, SEM-EDS, XPS and FTIR-DRIFTs techniques. Finely deposited silver crystallites sized in the range of 20–50 nm were observed through SEM and HR-TEM analysis. TPR and XRD studies demonstrated the presence of Ag2O and metallic silver (Ag0) on CZ support. About 10% of CO formation was observed on chelating catalyst (5Ag/CZ CHE). However, only, 5% CO was observed on impregnated (5Ag/CZ IMP) catalyst. The greater CO formation was associated with ease reduction of Ag2O to metallic silver in 5Ag/CZ CHE catalyst. Further, 70% of methanol selectivity was observed on 5Ag/CZ IMP due to the presence of Ag2O on CZ. FTIR-DRIFTs results revealed the methanol formation via formate intermediates and CO formation via RWGS reaction on the studied catalysts.

This work focuses on a novel synthesis route, using citric acid as a chelating agent, for the formation of gamma-Mo2N and Co3Mo3N bulk catalyst and their application for NH3 decomposition reaction for hydrogen production having its application for onboard generation of hydrogen for fuel cell in transportation vehicles. Successful formation of the pure bulk phase of Co3Mo3N was confirmed by using XRD, XPS, HRTEM techniques. The prepared Co3Mo3N catalyst showed high surface area 15.23 m(2)/g and high catalytic activity compared to bulk gamma-Mo2N for this decomposition reaction, having 97% conversion of NH3 at 550 degrees C at 6000 h(-1). (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Silicon nanoparticles (Si NPs) are highly attractive materials for typical quantum dots functions, such as in light-emitting and bioimaging applications, owing to silicon’s intrinsic merits of minimal toxicity, low cost, high abundance, and easy and highly stable functionalization. Especially nonoxidized Si NPs with a covalently bound coating serve well in these respects, given the minimization of surface defects upon hydrosilylation of H-terminated Si NPs. However, to date, methods to obtain such H-terminated Si NPs are still not easy. Herein, we report a new synthetic method to produce size-tunable robust, highly crystalline H-terminated Si NPs (4–9 nm) using microwave irradiation within 5 min at temperatures between 25 and 200 °C and their further covalent functionalization. The key step to obtain highly fluorescent (quantum yield of 7–16%) green-red Si NPs in one simple step is the reduction of triethoxysilane and (+)-sodium l-ascorbate, yielding routinely ∼1 g of H–Si NPs via a highly scalable route in 5–15 min. Subsequent functionalization via hydrosilylation yielded Si NPs with an emission quantum yield of 12–14%. This approach can be used to easily produce high-quality H–Si NPs in gram-scale quantities, which brings the application of functionalized Si NPs significantly closer.

A novel synthesis route, using citric acid as a chelating agent, for the formation of gamma-Mo2N and pure phase of Ni2Mo3N catalysts and their application for NH3 decomposition reaction for clean hydrogen production, have been performed. Successful formation of a pure bulk phase of Ni2Mo3N was confirmed by using XRD, XPS, HRTEM techniques and found that Ni2Mo3N is not air sensitive. Ni2Mo3N catalyst showed very high catalytic activity for NH3 decomposition reaction having similar to 97% conversion of NH3 at 525 degrees C at 6000 h(-1) GHSV, better than previously reported results on any non-promoted, non-precious catalysts, which is mainly due to the formation of pure phase and high surface area for this catalyst using a chelating method of preparation. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Oxides of chromium (Cr), molybdenum (Mo), or tungsten (W) were supported on mixed oxides of cerium and zirconium (CeO2-ZrO2) by an incipient wetness impregnation process, and used to investigate their activities for partial oxidation of methanol. High Resolusion Transmission Electron Microscope (HR-TEM) revealed that nanoparticles of Cr2O3, MoO3 or WO3 were formed on the CeO2-ZrO2 support. The particle sizes of Cr2O3, MoO3 and WO3 were 2-4, 3-6 and 4-5 nm, respectively. As a result of partial oxidation of methanol at 275 – 450 °C, formaldehyde (CH2O) was obtained as the major product over all these catalysts. Cr2O3 supported on CeO2-ZrO2 produced both CO and CO2 along with H2 production, while MoO3 and WO3 on CeO2-ZrO2 support generated only CO as a by-product. It was found that MoO3 supported on CeO2-ZrO2 showed the highest methanol conversion and CH2O yield among these three catalysts.

The aim of this work is to understand the catalytic behaviour of Li and Cs promoted Mo2N for CO hydrogenation to hydrocarbons and oxygenates at the reaction conditions 275-325 degrees C, 7MPa, and 30000h(-1) GHSV. Molybdenum nitrides were synthesized via temperature programmed treatment of ammonium heptamolybdate (AHM) and alkali metal (AM) precursors under continuous gaseous ammonia flow. Unpromoted Mo2N and AM-Mo2N catalysts were characterized using BET-pore size, X-ray diffraction, TPD-mass of CO, HR-TEM, and XPS techniques. Nominal loadings of 1, 5, and 10wt% of Li and Cs were selected for these studies. At a 10% CO conversion level, the total oxygenate selectivity of 28, 11, and 6.5% was observed on 5Cs-Mo2N, 5Li-Mo2N, and unpromoted Mo2N, respectively. The decreased oxygenate selectivity for unpromoted Mo2N was mainly associated with CO dissociative hydrogenation on Mo+ sites. On the other hand, improved molecular CO insertion into -CxHy intermediate accelerates the total oxygenate formation on the Cs-Mo-N catalyst. However, during nitridation, crystal structure changes were observed in Li-Mo-N and the obtained oxygenates selectivity was attributed to the Li2MoO4 phases. At lower AM loadings, the active sites corresponding to oxygenates formation were inadequate, and at higher AM loadings, surface metallic molybdenum decreased the total oxygenate selectivity.