1,721,004 research outputs found
Tetrazole-Substituted isomeric ruthenium polypyridyl complexes for low overpotential electrocatalytic CO2 reduction
No full textIntroducing tetrazole moiety to the ligand framework of two isomeric ruthenium catalysts, cis/trans-[Ru(tpy)(mtzp)(CH3CN)]2+ (tpy = 2,2′:6′,2′'-terpyridine, mtzp = 2-(1-methyl-1H-tetrazol-5-yl)pyridine), for the electrochemical reduction of CO2 to CO has altered the catalytic pathway with significantly low overpotential (0.37 V) compared to its analogous catalysts. Without manipulating steric effects, only the electronic nature of tetrazole moiety enables CO2 binding to ruthenium center to form metallocarboxylate intermediate just after one-electron reduction. This is the first synthesized isomeric pair of ruthenium complex follow ECE (E = electron transfer, C = chemical reaction) mechanism for electrocatalytic reduction of CO2. By successful characterization of the Ru–CO intermediate with the help of 13C NMR, spectro-electrochemical studies and analysis of byproducts formed during the electrocatalysis, a mechanism of CO2 reduction has been established in presence of water and anhydrous conditions which is further supported by density functional theory (DFT). © 2021 Elsevier Inc
Phosphomolybdic acid embedded into biomass-derived biochar carbon electrode for supercapacitor applications
Full text linkIn high-performance, clean, safe, and cost-effective ways, supercapacitors are among the most promising ways to store and release nonfossil energy. In recent years, renewable biomass-derived activated carbon has been explored as a potential option for electrode material. It restricts their specific capacitance despite being environment-friendly and possessing intrinsic mechanical strength. In order to overcome this limitation and preserve all other properties, we are infusing polyoxometalate into the activated carbon; this increases specific capacitance with its fast reversible redox behaviour and preserves the carbon's characteristics. Beside suffusing phosphomolybdic acid (PMA) into biomass waste material, such as orange peel-derived activated carbon (OPAC), a new hybrid material (OPAC-PMA) was developed. The nanohybrid design was revealed by structural and morphological research, which showed high interfacial contact, allowing polyanions to redox rapidly. The novel hybrid electrode material (OPAC-PMA) has a capacitance value of 66% higher than the bare OPAC electrode. A further study showed that OPAC-PMA composite showed 88.23% cycle stability in 0.5 M H2SO4 electrolyte at 6 A g−1 for 4000 cycles
Boron-induced controlled synthesis of Co-nano particles over Bx(CN)y matrix for CO hydrogenation in aqueous media
Full text linkBx(CN)y supported cobalt nanoparticles have been synthesized by regulating the ratios of melamine and boric acid precursors. The carbonization step is adequate to generate the desired controlled-sized cobalt particles at an auto-reduced state that can eliminate the requirement of promotors (e.g., Pt) for the hydrogen-spillover effect. The presence of nitrogen in support enhances the dispersion of cobalt particles by providing sites for cobalt to nucleate and grow due to the interaction between cobalt and Π electrons from the sp2-N center. Boron in the catalyst system significantly stabilizes the catalyst, thus improving its lifetime. However, the excess of boron promotes the aggregation of cobalt particles; therefore, optimal boron loading is preferable. Moreover, the binding energy calculation of Co6 over the B-doped and undoped C3N4 surface computed through DFT studies shows a reduction in metal-support interaction with the addition of boron, which leads to the aggregation of the cobalt particles with high boron. Overall, the catalyst with the optimized boron and nitrogen-containing support-stabilized cobalt particles is highly efficient in the aqueous phase Fischer-Tropsch synthesis
Characterization and Reactivity of TiO2/SiO2 Supported Vanadium Oxide Catalysts
No full textSeveral TiO2/SiO2 supports and supported vanadium oxide (vanadia) catalysts of varying titania and vanadia content are synthesized and characterized. Titania rutile phase is not detected for the TiO2/SiO2 supports even up to a calcinations temperature of 1073 K. The supported vanadia catalysts were also studied for the ethane and propane ODH reaction and compared with TiO2 (Degussa P25) supported catalysts. Surface vanadia species are present on the titania or silica part of the TiO2/SiO2 support depending on the titania and vanadia loading of the catalyst. Depending on the vanadia loading in the V2O5/TiO2/SiO2 catalyst the anatase to rutile phase transformation may occur below 1073 K. Furthermore, the ODH activity is retained or decreases less rapidly compared to the TiO2 supported catalyst as the calcination temperature is increased. Consequently, the TiO2/SiO2 supported vanadia catalysts do provide certain advantages compared to the TiO2 (Degussa P25) supported system
Synthesis of Porous Vanadia-Titania Catalyst for Oxidative Dehydrogenation of Propane
No full textA novel synthesis procedure has been applied for the synthesis of mesoporous vanadia-titania catalysts with varying vanadium content in the presence of P123 triblock copolymer as a structure directing agent. The synthesized mesoporous materials exhibited large pore diameter (∼9 nm) and high surface area (120–180 m2/g). Only anatase phase of titania was present in all the samples. Detailed characterization studies suggest the presence of molecularly dispersed reducible surface vanadium oxide species. XPS and 51V NMR results indicate that vanadium species on titania exist primarily in the oxidation state of V5+ and in V2O5 coordination with a form of distorted octahedral. The resulting mesoporous vanadia-titania catalysts are active in the oxidative dehydrogenation (ODH) of propane
Enhanced selectivity of benzene-toluene-ethyl benzene and xylene (BTEX) in direct conversion of n-butanol to aromatics over Zn modified HZSM5 catalysts
No full textThe sustainable aromatics production from renewable source is indispensable to circumvallate the dependence on fossil fuel for commodity chemicals. Direct conversion of n-butanol to aromatics using xZn-HZSM5 (0–10 wt%, SiO2/Al2O3 = 23, 55 and 280) catalysts was proposed in the present investigation. Characterization studies revealed the formation of different Zn species depending on the Zn loading. Furthermore, XPS analysis confirmed strong interaction of Zn species with the electronegative oxygen atom of zeolite framework. Zn deposition enhanced the selectivities of aromatics and BTEX. The presence of Zn species suppressed the hydride transfer reaction and promoted the dehydrogenation reaction resulting in higher selectivities of aromatics and BTEX. The rising temperature and declining in WHSV enhanced the selectivities of aromatics and BTEX. The high pressure had adverse effect on the selectivities of aromatics. The maximum selectivity of total aromatics (74.83%) and BTEX (68.75%) were achieved at 723 K, 1 bar pressure and 0.75 h−1 of WHSV. The coke analysis revealed the formation of polynuclear aromatic coke at high pressure. The alkyl substitute aromatics and polynuclear aromatics were formed predominately on pure HZSM5 (55) than 5Zn-HZSM5 (55). A plausible reaction mechanism was suggested considering the products distribution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Hydrodeoxygenation of Lignin Monomer Guaiacol Over Supported Bimetallic Nickel-Iron Catalysts to Produce Valuable Chemicals
No full textUpgradation of Lignin derived bio-oil and Liginin depolymerization stream to chemicals of industrial importance by catalytic hydrodeoxygenation (HDO) has garnered a lot of attention in many research studies. However, development of suitable catalysts with superior catalytic activity for deoxygenation, less H2 requirments and are also inexpensive is a challenging task. In this present work, we screened bimetallic nickel-iron (Ni-Fe) catalysts supported on zirconia (ZrO2) of varying Ni to Fe mole ratio synthesized by co-impregnation method with an aim to develop a novel inexpensive catalyst for guaiacol HDO. All the synthesized catalysts were analysed using characterization techniques such as BET, XRD (powder), H2-TPR, UV-vis, FTIR and pyridine-FTIR. We have investigated the effect of reaction parameters on product distribution and conversion of guaiacol over a wide range of reaction temperature (523 to 623 K), initial hydrogen pressure (0 to 40 bar H2), catalyst loading (0 to 1 % (wt/v)), varying Ni to Fe mole ratio and total metal loading (2 to 7 wt%) and optimized all these parameters. Bimetallic 5Ni1Fe1/ZrO2 catalyst demonstrated superior catalytic activity than monometallic 5Ni1Fe0/ZrO2 and 5Ni0Fe1/ZrO2 with 60% selectivity to phenol and this can be attributed to the synergistic effects of Ni and Fe in bimetallic catalyst. Phenol was found to be major primary product upon which it is further transformed to cyclohexanol, cyclohexanone, cyclohexane, benzene and cresols with varying selectivities depending upon the active metal species dispersed on the catalyst surface. 5Ni1Fe0/ZrO2 catalyst exhibited a higher affinity for aromatic ring hydrogenation and there by yielding cyclohexane as major product whereas on the other hand 5Ni0Fe1/ZrO2 yielded phenol as major product. Upon increaing the Fe content in bimetallic Ni-Fe catalysts resulted in decreased selectivity towards ring hydrogenation products and thus demonstrating the ability of Fe to suppress the ring hydrogenation reactions as reported in the literature earlier. Upon studying the time distribution of products of guaiacol HDO under broad range of reaction parameters with catalysts of varying Ni to Fe mole ratio, we have come up with possible reaction pathways involved in guaiacol HDO and reaction mechanism for HDO of guaicol has been proposed
Production of aromatics from butanol over Ga-promoted HZSM5 catalysts: tuning of benzene–toluene–xylene and ethylbenzene (BTEX) selectivity
No full textThe present investigation demonstrates the conversion of n-butanol to aromatics (BTA) including building block aromatics in one step over Ga modified HZSM5 catalysts in a fixed bed reactor under varying process parameters (temperature, pressure, and weight hourly space velocity, WHSV). The several Ga modified HZSM5 catalysts prepared by the incipient wetness impregnation method were well characterized by several techniques. The different gallium species (GaO+ and Ga+ species) formed on Ga-HZSM5 catalysts, as confirmed by the characterization results, behave as Lewis acid sites, which played a crucial role in the enhancement of the dehydrogenation reaction and suppression of the hydride transfer reaction leading to the production of different aromatics. Specifically, the selectivity to benzene, toluene, ethylbenzene, and xylenes (BTEX) was enhanced on deposition of Ga on the HZSM5 catalyst. The selectivity to different aromatics was also affected by the variation of different process parameters. The total aromatics selectivity was raised with increasing temperature and decreasing WHSV. However, the aromatics production was reduced at high operating pressure. The high operating pressure led to the production of higher aromatics and deposition of these aromatics caused the deactivation of the catalyst. Characterization of spent catalysts confirmed the deposition of polynuclear aromatics as hard coke. The maximum total aromatics selectivity of 76.0% (BTEX 69.2%) was achieved for the 5Ga-HZSM5 catalyst at 823 K, 0.75 h−1 WHSV, and 1 atm. A comprehensive reaction pathway was recommended considering the product distribution obtained under the studied reaction conditions. © 2022 The Royal Society of Chemistr
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