Vanadium Catalysts Research Articles

Life cycle sustainability assessment of optimized biodiesel production from used rice bran oil employing waste derived-hydroxyapatite supported vanadium catalyst.

The present work encompasses the production of biodiesel from an inexpensive waste, viz., used rice bran oil (URBO) through concurrent esterification and transesterification reactions employing the prepared waste duck bone (WDB)-derived natural hydroxyapatite (NAHAp) supported vanadium impregnated solid catalyst (VNAHAp). The optimal VNAHAp catalyst possessed 92.23 m2/g surface area which was much superior to 61.46 m2/g of the V-catalyst (VCHAp) prepared using commercially available hydroxyapatite (CHAp). The optimal (Box-Behnken design) concurrent trans/esterification reaction conditions for biodiesel (FAME) production from URBO and methanol were 5 wt.% catalyst concentration, 8:1 methanol/URBO mole ratio, and 35 wt% NH4VO3 loaded VNAHAp (35VNAHAp) catalyst that resulted in 99.05% FAME yield deploying a low-energy infrared radiator assisted batch reactor (LIRABR) which ensured significantly high FAME yield at milder temperature (60°C) and in shorter reaction time (30 min) compared to a conventionally heated batch reactor. The product biodiesel and its blend with commercial diesel conformed to ASTM D7467-10 specifications. The life cycle assessment (LCA) of the entire process advocated superior sustainability of the biodiesel production using 35VNAHAp catalyst in the LIRABR compared to their conventional counterparts. Valorization of two potential wastes, viz., URBO and WDB, under milder process conditions involving LIRABR and 35VNAHAp resulted in lower environmental impacts, thus rendering a sustainable biodiesel production process towards a greener earth.

Supported Vanadium Catalysts for Selective Sulfur‐Oxidative Dehydrogenation of Propane

AbstractThe catalytic oxidative dehydrogenation of propane (ODHP) is a challenging reaction due to facile competing overoxidation to COx. The gaseous disulfur molecule, S2, is isoelectronic with O2 and has been shown to act as an alternative, “soft oxidant” for the analogous process (SODHP) over bulk metal sulfide catalysts. However, these bulk catalysts suffer from low surface areas and ill‐defined active sites – issues that might be addressed with a supported catalyst. Here we investigate supported V/Al2O3 materials for SODHP. We show that these catalysts are highly selective for propylene, far surpassing the yields of the prior bulk systems. Isolated sulfided vanadium species are found to be more active and selective than crystalline vanadium sulfide. Additionally, we compare the S2 and O2 oxidants over sulfided and calcined V/Al2O3 materials, respectively, and find that the propylene selectivity is enhanced using S2 as the oxidant. These results suggest that sulfur is a promising soft oxidant that can be used to achieve high propylene selectivities over supported metal sulfides.

Naturally Occurring Oxazole Structural Units as Ligands of Vanadium Catalysts for Ethylene-Norbornene (Co)polymerization

1,3-Oxazole and 4,5-dihydro-1,3-oxazole are common structural motifs in naturally occurring peptides. A series of vanadium complexes were synthesized using VCl3(THF)3 and methyl substituted (4,5-dihydro-1,3-oxazol-2-yl)-1,3-oxazoles as ligands and analyzed using NMR and MS methods. The complexes were found to be active catalysts both in ethylene polymerization and ethylene-norbornene copolymerization. The position of methyl substituent in the ligand has considerable impact on the performance of (co)polymerization reaction, as well as on the microstructure, and thus physical properties of the obtained copolymers.

Redox and acid properties of MnV2Ox/TiO2 catalysts synthesized by assistance of microwave for NO selective catalytic reduction by ammonia

Supported manganese vanadate catalysts for selective catalytic reduction of NOx by ammonia (NH3-SCR) with wide temperature window were fabricated by assistance of microwave. Vanadate dispersed well on the surface of TiO2, giving an enhanced activity in a wide temperature range. The activity over the catalyst at low temperatures enhanced as vanadate loading increased, deriving from the promoting redox property and the lowering stability of adsorbed NH3 species. The in situ DRIFT results indicated that NH3-SCR reaction over the well dispersed vanadate catalyst follow the “Eley-Rideal” (E-R) mechanism for the effective adsorption of NH3. The results showed the potential applications of this kind of catalyst for NOx elimination in some certain conditions.

Selective Catalytic Oxidation of Lean-H2S Gas Stream to Elemental Sulfur at Lower Temperature

Ceria-supported vanadium catalysts were studied for H2S removal via partial and selective oxidation reactions at low temperature. The catalysts were characterized by N2 adsorption at 77 K, Raman spectroscopy, X-ray diffraction techniques, and X-ray fluorescence analysis. X-ray diffraction and Raman analysis showed a good dispersion of the V-species on the support. A preliminary screening of these samples was performed at fixed temperature (T = 327 °C) and H2S inlet concentration (10 vol%) in order to study the catalytic performance in terms of H2S conversion and SO2 selectivity. For the catalyst that exhibited the higher removal efficiency of H2S (92%) together with a lower SO2 selectivity (4%), the influence of temperature (307–370 °C), contact time (0.6–1 s), and H2S inlet concentration (6–15 vol%) was investigated.

A Robust Vanadium(V) Tris(2-pyridyl)borate Catalyst for Long-Lived High-Temperature Ethylene Polymerization

Soluble vanadium catalysts are highly coveted for their selectivity in olefin polymerization. However, their utility is limited by rapid deactivation, especially at scalable temperatures under which the polymer remains soluble (>100 °C). Reasoning that a highly σ-donating scorpionate ligand would stabilize the vanadium(V) against reductive deactivation, we developed vanadium tris(2-pyridyl)borate complexes and studied their reactivities in high-temperature homogeneous ethylene polymerization. Complex 1 shows exceptional ethylene polymerization longevity at high temperatures, with 1 h of activity at 105 °C. The low polydispersity, vinyl end groups, and concentration effects indicate single-site catalysis involving chain transfer to the monomer. These results provide a new platform for studying high-valent vanadium catalysts under demanding conditions.

CO2 as a soft oxidant for propane oxidative dehydrogenation: A mechanistic study using operando UV Raman spectroscopy

The utilization of CO2 as an oxidant has recently attracted increasing attention due to its mild oxidizing properties allowing higher product selectivities to be achieved e.g. in propane oxidative dehydrogenation (ODH). In this communication we address mechanistic aspects of propane ODH over silica supported vanadia (VOx/SiO2) catalysts in the presence of CO2 as oxidizing agent. The use of operando UV Raman spectroscopy reveals distinct changes in the surface vanadia structure including breakage of VOV bonds and a partial reduction of vanadyl, as well as the formation of support hydroxyl groups, while the presence of CO2 is observed to prevent coke deposition. Our results are fully consistent with the occurrence of two parallel pathways, i.e., direct ODH (one step) and dehydrogenation followed by a reverse water-gas shift reaction (two step), supporting previous literature proposals.

Synthesis of Cyclic Polyolefin: Ring‐Opening Metathesis Polymerization by Binuclear Vanadium Complexes†

Main observation and conclusionRing‐opening metathesis polymerization (ROMP) of norbornene by binuclear vanadium alkylidene in‐situ formed from dialkyl complexes was investigated. Higher activities were observed by the binuclear system than mononuclear analogues. Especially the cyclic polymers were obtained and demonstrated. It is proposed that cyclic binuclear vanadium alkylidene was afforded due to the intramolecular chain‐transfer reaction. The size of polymer ring could be adjusted by the vanadium catalyst structure and polymerization temperature. Similar results were also observed in the ROMP of cyclopentene.

The active role of the support in propane ODH over VOx/CeO2 catalysts studied using multiple operando spectroscopies

Because of the relevance of supported vanadia catalysts for the oxidative dehydrogenation (ODH) of alcohols and short alkanes, a detailed mechanistic understanding, including the role of the support, is of great importance. In this work, we address the ODH of propane over ceria-supported vanadia (VOx/CeO2) catalysts, especially regarding the active participation of ceria and the synergy effect between ceria and vanadia. A combination of operando multi-wavelength Raman-, operando UV-Vis- and operando IR spectroscopy is applied, including the targeted use of different Raman excitation wavelengths to selectively enhance vibrational features through resonance from vanadia (514 nm) and the ceria support (385 nm). Our operando results show that surface lattice oxygen from ceria is crucial for the selective oxidation of propane while the structure of vanadia seems to stay unchanged during the reaction. Rather vanadia structures play an indirect role in increasing the overall selectivity of the reaction. The surface oxygen defects of ceria are affected by the interaction with vanadia monomeric species in direct proximity, owing to an irreversible occupancy of the vacancies by vanadia monomers, which slows down the overall oxygen dynamics and thereby decreases the amount of CO2 produced. Dimeric and oligomeric vanadia species weaken the adsorption of propane onto the ceria surface, further increasing the selectivity. Our mechanistic insights demonstrate the synergy effect between vanadia and ceria in oxidation reactions and provide an experimental basis for a detailed understanding of the role of the support in VOx/CeO2 and other supported vanadia catalysts.

Ca-Poisoning Effect on V2O5-WO3/TiO2 and V2O5-WO3-CeO2/TiO2 Catalysts with Different Vanadium Loading

Ca poisoning behavior is inevitable for high-calcium content flue gas, so V2O5-WO3/TiO2 (VWT) and V2O5-WO3-CeO2/TiO2 (VWCeT) catalysts with different vanadium content have been prepared and the Ca-doped catalysts are compared in this manuscript. The result shows Ce addition can both promote the NO conversion and the alkali resistance. Lower Ca addition for 0.1VWCeT catalyst promotes its oxidability and Ce modification is more suitable for low vanadium catalysts. The total acidity and the reducibility of catalysts decline after Ca doping, and the reducibility of the active species on catalysts has been strengthened by Ce addition. CeO2 based catalysts with lower Ca loading struggle to resist sulfur poisoning, while higher Ca loading favors SO2 adsorption and also physically reduces the cerium acidification process. In the presence of SO2, additional Brønsted acid sites are formed in Ca rich catalyst. The dynamic NH3 adsorption has been investigated, shows that Ca doping content on catalyst is critical for SCR reaction, and the catalyst is more susceptible to SO2 initially in alkali flue gas during the actual application, but the sulfur resistance may increase with the alkali-poisoning effect aggravated by Ca doping.

Bimodal effect of water on V2O5/TiO2 catalysts with different vanadium species in the simultaneous NO reduction and 1,2-dichlorobenzene oxidation

VOX/TiO2 catalysts with different vanadium loading were prepared in order to study the influence of vanadium species on the effect of water in the simultaneous NO reduction through NH3-SCR and o-DCB oxidation reactions. The presence of isolated, polymeric and crystalline species and their redox and acid properties were evaluated by N2-Adsorption, XRD, Raman, H2-TPR, XPS and NH3-TPD. Water has a bimodal and reversible effect in both NO reduction and o-DCB oxidation depending on vanadium species and temperature. In SCR, water has a detrimental effect at low temperature due to competitive adsorption with NO and NH3, while at high temperature it promotes an increase of NO conversion associated to the suppression of side-reactions, which increase the selectivity towards N2. In o-DCB oxidation, the effect of water is the sum of two contributions: one positive, related to the removal of surface adsorbed detrimental species; and one negative, associated to the competitive adsorption with o-DCB. Thus, at high temperature water acts as inhibitor, while at low temperature water has a promotional effect in the highly dispersed vanadium catalysts due to their tendency to suffer deactivation, mainly by carbonaceous materials. The presence of water also favors total oxidation and decreases the formation of chlorinated by products.

Bis(phenolate)-functionalized N-heterocyclic carbene complexes of oxo- and imido-vanadium(V)

Oxo- and imido-vanadium(V) metal complexes supported by bis(phenolate)-functionalized N-heterocyclic carbene (NHC) ligands were synthesized and structurally identified. In the presence of [(Ph3P)2N]Cl ([PPN]Cl), saturated NHC oxo-vanadium complexes showed activity in the coupling of CO2 and cyclohexene oxide (CHO) into cis-cyclohexene carbonate (cis-CHC). More importantly, the oxo-vanadium complex bearing the less electron-donating benzannulated NHC ligand was found to be more active in CHO conversion to poly(cyclohexene carbonate) (PCHC) in addition to the cis-CHC, highlighting the beneficial effect of the weak electron-donating ability of the latter vs. saturated NHC ligands within such vanadium catalysts. Evaluation of the saturated NHC imido-vanadium catalyst performance led to the same activity and selectivity as the analogous oxo-vanadium catalysts owing to its reactivity with CO2 via a [2 + 2] cycloaddition reaction forming an oxo-vanadium species.

Simple physical mixing of zeolite prevents sulfur deactivation of vanadia catalysts for NOx removal

NOx abatement has been an indispensable part of environmental catalysis for decades. Selective catalytic reduction with ammonia using V2O5/TiO2 is an important technology for removing NOx emitted from industrial facilities. However, it has been a huge challenge for the catalyst to operate at low temperatures, because ammonium bisulfate (ABS) forms and causes deactivation by blocking the pores of the catalyst. Here, we report that physically mixed H-Y zeolite effectively protects vanadium active sites by trapping ABS in micropores. The mixed catalysts operate stably at a low temperature of 220 °C, which is below the dew point of ABS. The sulfur resistance of this system is fully maintained during repeated aging/regeneration cycles because the trapped ABS easily decomposes at 350 °C. Further investigations reveal that the pore structure and the amount of framework Al determined the trapping ability of various zeolites.

Front Cover Picture: Recent Developments in Z‐Selective Olefin Metathesis Reactions by Molybdenum, Tungsten, Ruthenium, and Vanadium Catalysts (8/2021)

The front cover picture, designed by K. Nomura and K. M. Dawood illustrates the basic mechanism for Z-selective (cis-specific) olefin metathesis by molybdenum, ruthenium and vanadium catalysts. The review includes reports for transition metal catalyzed Z-selective olefin metathesis reactions (EROCM, CM, ROMP, and RCM) applied for organic synthesis and polymer synthesis. The review also includes basic background in the catalyst design, ligand modifications, which play an essential role for the success. Details can be found in the review by Kamal M. Dawood and Kotohiro Nomura (K. M. Dawood, K. Nomura, Adv. Synth. Catal. 2021, 363, 1970–1997; DOI: 10.1002/adsc.202001117).

Verification of impurity-related photocatalytic activity of insulating oxide supports

Photocatalysts composed of vanadium oxide species supported on commercial MgO and ZrO2 are investigated in selective methanol oxidation. Both support oxides are insulators, so the vanadium oxide species are expected as sole active component in photocatalysis. However, the pure supports showed considerable activity: Bare MgO was more active than MgO-supported vanadia catalysts, and ZrO2 showed intermediate activity. By various characterization methods, the presence of TiO2 (anatase) in the MgO support, and the presence of Zn, possibly as ZnO, in ZrO2 is demonstrated. The present study highlights that photocatalysts containing commercial supports must be carefully checked for impurity-related photocatalytic performance.

Selective recovery of vanadium pentoxide from spent catalysts of sulfuric acid production: Sustainable approach

Spent vanadium catalysts of sulfuric acid production (main elemental composition in wt%: 7.5 V, 9.1 K, 10.2 S, 23.2 Si and 1.4 Fe) can be used as a secondary source of vanadium. Extraction of vanadium was studied using two-step leaching (acidic and reductive) of spent vanadium catalysts with further oxidizing of leaching solutions. The factors leaching and hydrolysis temperature, concentration of leaching (H2SO4, Na2SO3) and oxidizing ((NH4)2S2O8) reagents, solid/liquid ratio, mixing parameters, and time of leaching and thermohydrolysis were systematically investigated. The solubility of V2O5 was investigated as a function of temperature, pH of sulfuric acid solutions, and concentration of Na2SO3. The kinetics of V2O5 solubility and reduction were also studied. The vanadium leaching yield after a two-step recovery was 98 wt% after acidic (H2SO4, pH 1.2–1.3) leaching with ultrasonic treatment for 5 min at ambient temperature, followed by reductive leaching in 0.01 Mol/L Na2SO3 solution for 15 min at ambient temperature. The highest vanadium extraction yield from leaching solutions was 98 wt% obtained through oxidizing of leaching solutions by 30 wt%. (NH4)2S2O8 with a molar ratio n(V2O5)/n((NH4)2S2O8) of 5/1 for a reaction time of 5 min at 80–90 °C. the extracted vanadium product was V2O5 with a purity of 85–87 wt%. The technological scheme has been developed to recycle all obtained products and sub-products

Oxidative dehydrogenation of ethyl lactate to ethyl pyruvate over vanadium and iron antimonates catalysts

The oxidative dehydrogenation of ethyl lactate to ethyl pyruvate, corresponding to the first step of a new process in the industrial production of methionine, has been investigated. Iron and vanadium antimonates were developed as catalysts, and were optimized to reach 87 % conversion of ethyl lactate, with 88 % selectivity to ethyl pyruvate, at only 275 °C. The catalysts were characterized before and after catalytic testing, and in situ using various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and XANES spectroscopy. The results show that neither the Sb3+/Sb5+ nor the Fe2+/Fe3+ redox couple were involved in the dehydrogenation of ethyl lactate, or in the catalysts re-oxidation. The active and selective catalytic sites correspond to surface V5+ species. These species should not be considered as part of the bulk oxide, but as supra-surface species whose surface content is monitored with the bulk composition.

Recent Developments in Z‐Selective Olefin Metathesis Reactions by Molybdenum, Tungsten, Ruthenium, and Vanadium Catalysts

AbstractThis review article summarizes reports for Z‐selective olefin metathesis reactions by molybdenum, tungsten, ruthenium, and vanadium catalysts. It is clearly demonstrated that the ligand modifications play essential roles in achieving the stereospecific olefin metathesis reactions. In particular, Mo‐ and W‐alkylidene based complex catalysts having pyrrolide‐aryloxide [or bis(aryloxide)] were highly effective in the efficient enantioselective ring opening/cross‐metathesis (EROCM), cross metathesis (CM), homodimerization, ring‐opening metathesis polymerization (ROMP), and in ring closing metathesis (RCM) with high Z‐ selectivities (∼>98%). Ruthenium‐carbene catalysts having cycloadamantyl, catechothiolate, phenolate and thiophenolate ligands display pronounced Z‐selectivity (>98%) in efficient CM, ROCM, AROCM, RCM, ROMP reactions. Halogenated (arylimido)‐alkoxo vanadium‐alkylidenes were thermally robust and effective for efficient highly cis‐specific ROMP of cyclic olefins to afford end‐functionalized ring‐opened polymers.magnified image

A highly chlorinated xylene promoter for ethylene-propylene copolymerisation over a vanadium catalyst.

The regularities of ethylene–propylene copolymerisation over a vanadium oxytrichloride (VOCl3)–ethylaluminium sesquichloride (EASC) catalytic system in the presence of hexachloro-p-xylene (HCPX), tert-butyl chloride, trichlorotoluene, hexachlorocyclopentadiene, and trichloroacetate were studied. The main kinetic regularities of ethylene–propylene copolymerisation when using HCPX were determined and the kinetic parameters of the process were obtained. It was shown that hexachloro-p-xylene is the most efficient promoter of polymerisation that increases activity of the “vanadium” catalyst severalfold and enhances propylene reactivity in its copolymerisation with ethylene. A number of molecular characteristics and physicochemical parameters were determined for the synthesised samples of ethylene–propylene copolymers. The resulting copolymers have a higher molecular weight and a broad molecular weight distribution and are richer in propylene monomers compared to the copolymers synthesised in the catalytic system without HCPX. Modification of the “vanadium” catalyst yields the copolymer with a more homogeneous structure. Assumptions were made about the mechanism of action of the promoter under study in the VOCl3–EASC catalytic system.

Селективне каталітичне очищення вихлопних газів дизельних двигунів локомотивів від оксидів азоту на блочному волокнистому ванадієвому каталізаторі

Селективне каталітичне очищення вихлопних газів дизельних двигунів локомотивів від оксидів азоту на блочному волокнистому ванадієвому каталізаторі