Dehydrogenation Of 2-propanol Research Articles

Development of ruthenium complexes with S-donor ligands for application in synthesis, catalytic acceptorless alcohol dehydrogenation and crossed-aldol condensation.

The reaction of [Ru(dmso)4Cl2] with a potassium salt of four xanthate (RO-C(S)S-; R = Me, Et, iPr and tBu) ligands (depicted as Ln; n = 1-4) in hot methanol afforded a group of mixed-ligand complexes of type [Ru(Ln)2(dmso)2]. The crystal structures of all the four complexes have been determined, which show that the xanthate ligands are bound to the metal center forming four-membered chelates and dmso is coordinated through sulfur and they are mutually cis. The relative thermodynamic stability of this cis and the other possible trans-isomers of these complexes has been assessed with the help of DFT calculations, which have revealed that the cis-isomer is the more stable isomer. The coordinated dmso in the [Ru(Ln)2(dmso)2] complexes could be easily displaced by chelating bidentate ligands (depicted as L') to furnish complexes of type [Ru(Ln)2(L')], as demonstrated through isolation of two such complexes, viz. [Ru(L3)2(bpy)] and [Ru(L2)2(phen)] (bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline). The crystal structure of [Ru(L3)2(bpy)] has been determined and the structure of [Ru(L2)2(phen)] has been optimized by the DFT method. The electronic spectra of the four [Ru(Ln)2(dmso)2] complexes and the two derivatives ([Ru(Ln)2(L')]; n = 3, L' = bpy; n = 2, L' = phen), recorded in dichloromethane solutions, show intense absorptions spanning the visible and ultraviolet regions, which have been analyzed by the TDDFT method. The [Ru(Ln)2(dmso)2] complexes are found to serve as efficient catalyst precursors for the acceptorless dehydrogenation of 2-propanol followed by crossed-aldol condensation with substituted benzaldehydes (and related aldehydes), using tert-butoxide as the co-catalyst, producing dibenzylideneacetone derivatives in good yields.

Synergistic contribution of metal–acid sites in selective hydrodeoxygenation of biomass derivatives over Cu/CoOx catalysts

The efficient hydrodeoxygenation (HDO) of biomass derivatives to yield specific products is a significant yet challenging task. In the present study, a Cu/CoOx catalyst was synthesized using a facile co-precipitation method, and subsequently used for the HDO of biomass derivatives. Under optimal reaction conditions, the conversion of 5-hydroxymethylfurfural reached 100% with a selectivity of ∼99% to 2,5-diformylfuran. In combination with the experimental results, systematic characterizations revealed that CoOx, as the acid site, tended to adsorb CO bonds, and the metal sites of Cu+ were inclined to adsorb CO bonds and enhance CO bond hydrogenation. Meanwhile, Cu0 was the main active site for 2-propanol dehydrogenation. The excellent catalytic performance could be attributed to the synergistic effects of Cu and CoOx. Further, by optimizing the ratio of Cu to CoOx, the Cu/CoOx catalysts exhibited notable performance in HDO of acetophenone, levulinic acid, and furfural, which verified the universality of the catalysts in the HDO of biomass derivatives.

Lattice-charge imbalance and redox catalysis over perovskite-type ferrite- and manganite-based mixed oxides as studied by XRD, FTIR, UV–Vis DRS, and XPS

In the present investigation, two sets of pure and substituted ferrite- and manganite-based mixed oxides were prepared within the stoichiometric formulaA_{1 - x} A^{prime}_{x} B_{1 - x} B^{prime}_{x} O_{3}, where A = Bi or La, A′ = Sr, B = Fe or Mn, B′ = Co, x = 0 or 0.2, by calcination at 700 °C (for 1 h) of corresponding metal citrate xerogels. Materials thus obtained were examined for bulk and surface characteristics using X-ray diffractometry, ex situ Fourier transform infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and N2 sorptiometry. Their redox catalytic activity was evaluated towards a 2-propanol dehydrogenation reaction in the gas phase by employing in situ Fourier transform infrared spectroscopy. The results obtained could help reveal that (1) the presence of Bi (versus La) and Mn (versus Fe) facilitated the formation of polymeric crystalline phases assuming lattice-charge imbalance (due to excess positive charge), (2) the surface exposure of the excess positive charge was manifested in the generation of Mn sites having various oxidation states ≥ 3+, (3) the consequent development of visible light absorptions at 498–555 nm suggested occurrence of electron double-exchange facilitated by the formation of Mnn+–O2−–Mn(n+1)+ Zener-type linkages, and (4) the exposure of such linkages at the surface warrants the establishment of the electron-mobile environment necessitated by the redox catalytic activity. Moreover, the relationship between the alcohol dehydrogenation activity and the magnitude of the lattice-charge imbalance (i.e., the net excess positive charge) of the catalysts was highlighted.

Insights into the Hydrogenolysis Mechanism of Diphenyl Ether over Cl-Modified Pt/γ-Al2O3 Catalysts by Experimental and Theoretical Studies

Catalytic hydrogenolysis is an efficient method for converting lignin-derived aryl ethers into monoaromatic products by cleaving the C–O bond and maintaining the phenyl rings. However, it is difficult to obtain aromatics with high selectivity because ring hydrogenation proceeds in parallel. Herein, we showed that a Cl-modified Pt/γ-Al2O3 catalyst exhibited higher selectivity for aromatics (91.6%) compared to unmodified Pt/γ-Al2O3 (3.9%) in C–O bond cleavage of diphenyl ether (DPE, 4-O-5 linkage in lignin). Characterization of the catalysts and density functional theory (DFT) calculations indicated that the Cl species preferred to localize at the terrace sites of Pt nanoparticles (NPs). Due to the decrease in the number of active sites, the Cl-modified Pt/γ-Al2O3 catalyst exhibited low activity for 2-propanol dehydrogenation, and thus the catalytic activity for the hydrogenation of aromatic products was suppressed. On the other hand, DPE adsorbed at the low coordination site, which caused the phenyl rings to move away from the metal surface; this configuration was unfavorable for the hydrogenation reaction. According to DFT calculations, the high selectivity for benzene was mainly attributed to the lower energy barrier for C–O bond cleavage of phenol at the low-coordination sites.

Synthesis of Cu/SiO2(MCM-41) mesostructured catalysts. Effect of the preparation method on the textural properties and chemical structure

Two Cu/SiO2 mesoporous materials (Cu-MCM-41) were synthesized, one by the ion exchange (IE) post-synthesis method and the other, by the sol-gel (SG) method by co-precipitation of copper and silica (Cu-MCM-41) in the cetyltrimethylammonium bromide (CTAB) presence. The effects of the synthesis method on these materials were analyzed. They were characterized by XRD, N2 adsorption-desorption, TEM, DRUV–vis, FTIR, TPR, XPS, and FTIR with both, CO and pyridine adsorbed. Using the SG method, an MCM-41 material with a uniform mesoporous structure (Dp ≈ 35 Å), and a specific surface area (SBET) of 800 m2.g-1, was obtained. With the IE method and due to the partial collapse of the SiO2-MCM-41 mesoporous structure used as support, a material with a lower SBET (560 m2.g-1) was produced. The Cu in the SG synthesized material was mainly constituted by SiO-[CuO]n-CuOSi polymeric species and small CuO agglomerates. On the other hand, in the IE material, the copper was in the form of isolated SiO–Cu–OSi monomers, SiO–Cu–O–Cu–OSi dimers, and only a low proportion of SiO-[CuO]n-CuOSi oligomers. The catalytic activity of both materials was tested against the 2-propanol (2-PrOH) dehydrogenation in the gas phase. The reaction rate of the IE synthesized material was an order of magnitude higher than that prepared by the SG method. This behavior was attributed to the presence of SiO–Cu+ pair formed by the reduction of SiO–Cu–O–Cu–OSi dimmers present in the material prepared by IE; in contrast with the CuO aggregates obtained by the SG method.

Tuning dual active sites of Cu/CoCeOx catalysts for efficient catalytic transfer hydrogenation of 5-hydroxymethylfurfural to biofuel 2,5-dimethylfuran

Much attention has been attracted on the production of renewable biofuels through efficient catalytic transfer hydrogenation (CTH) reaction. In this study, a series of Cu/CoCeOx catalysts were synthesized by a facile coprecipitation method for CTH of 5-hydroxymethylfurfural (HMF) to different products with 2-propanol as a hydrogen donor, and the dual active sites of CuCo and CoCeOx were tuned via H2-reduction temperature. A 92.2% yield of 2,5-dihydroxymethylfuran (DHMF) was achieved at 150 °C over the Cu4Co8Ce4-300 catalyst, and a 95.4% yield of 2,5-dimethylfuran (DMF) was obtained over the Cu4Co10Ce2-600 catalyst at 170 °C. The roles of the dual active sites were further investigated, and the results showed that Cu species were identified as the major active sites of 2-propanol dehydrogenation, CoCeOx sites were responsible for the conversion of HMF to DHMF, and CuCo bimetallic nanoparticles promoted the cleavage of C-O in DHMF to obtain DMF. XRD, Raman, and HAADF-STEM analysis confirmed the existence of these sites. XPS and H2-TPR verified the formation of CuCo bimetallic nanoparticles, and NH3-TPD was employed to evaluate the acidity of the surface. Furthermore, in situ DRIFT of furfuryl alcohol and performance test experiments were conducted to understand the synergistic mechanism of dual active sites in hydrogen transfer from 2-propanol to HMF. This work provides a strategy to obtain different target products via tuning dual active sites.

Sustainable Process Design for Acetone Purification Produced via Dehydrogenation of 2-Propanol

Acetone purification is one of the most critical stages of its production process, because a large amount of energy is required. Due to this high energy consumption, the process turns out to be not very sustainable and not friendly to the environment. In this sense, the development of intensified alternatives that minimize energy consumption in this process is of utmost importance. Besides, the safest possible processes are sought, so it is necessary that the control properties of these novel processes be studied at an early design stage. This work proposes two new intensified systems for the purification of acetone; the intensified schemes are a thermally coupled distillation system with a side rectifier and a Petlyuk arrangement. The results indicate that in this type of systems where interconnection flows are used, the magnitudes of these flows have a direct impact on energy consumption, because lower values of interconnection flows as in the case of the thermally coupled system achieve a reduction, whereas higher values as in the case of the Petlyuk system have a negative impact. As for the control properties, the intensified schemes present better values of the condition number with respect to the conventional design, because the interconnection flows reduce the disturbance of the manipulable variables. On the other hand, if the feed is disturbed, the interconnection flows generate an increase in the disturbance in the system, obtaining that the conventional system presents the best values. Therefore, making a balance between the studied designs and looking for a system that presents the best sustainability indicators, the thermally coupled system obtains the best results with a 25.92% energy saving and CO2 emission reduction with respect to the conventional system and acceptable values for the control and safety indexes.

Durability and activity of Co2YZ (Y = Mn or Fe, Z = Ga or Ge) Heusler alloy catalysts for dehydrogenation of 2-propanol

Using dehydrogenation of 2-propanol as a test reaction for Heusler alloy catalysts, durability against oxidation and a relationship between activity and electronic structures were revealed.

Tris(2-Aminoethyl)Amine/Metal Oxides Hybrid Materials-Preparation, Characterization and Catalytic Application.

Three different metal oxides (basic MgO, basic-acidic Al2O3 and acidic-basic Nb2O5) characterized by comparable surface areas (MgO—130 m2/g; Al2O3—172 m2/g and Nb2O5—123 m2/g) and pore systems (domination of mesopores with narrow pore size distribution) were modified with tris(2-aminoethyl)amine (TAEA) via two methods: (i) direct anchoring of amine on metal oxide and (ii) anchoring of amine on metal oxide functionalized with (3-chloropropyl)trimethoxysilane. The obtained hybrid materials were characterized in terms of effectiveness of modifier anchoring (elemental analysis), their structural/textural properties (nitrogen adsorption/desorption, XRD), acidity/basicity of support (2-propanol dehydration and dehydrogenation, dehydration and cyclization of 2,5-hexanedione), states of modifier deposited on supports (XPS, FTIR, UV–VIS) and the strength of interaction between the modifier and the support (TG/DTG). It was evidenced that acidic-basic properties of metal oxides as well as the procedure of modification with TAEA determined the ways of amine anchoring and the strength of its interaction with the support. The obtained hybrid materials were tested in Knoevenagel condensation between furfural and malononitrile. The catalysts based on MgO showed superior activity in this reaction. It was correlated with the way of TAEA anchoring on basic MgO and the strength of modifier anchoring on the support. To the best of our knowledge tris(2-aminoethyl)amine has not been used as a modifier of solid supports for enhancement of the catalyst activity in Knoevenagel condensation.

Probing the temperature of supported platinum nanoparticles under microwave irradiation by in situ and operando XAFS

Microwave irradiation can cause high local temperatures at supported metal nanoparticles, which can enhance reaction rates. Here we discuss the temperature of platinum nanoparticles on γ-Al2O3 and SiO2 supports under microwave irradiation using the Debye–Waller factor obtained from in situ extended X-ray absorption fine structure (EXAFS) measurements. Microwave irradiation exhibits considerably smaller Deby–Waller factors than conventional heating, indicating the high local temperature at the nanoparticles. The difference in the average temperatures between the platinum nanoparticles and the bulk under microwaves reaches 26 K and 132 K for Pt/Al2O3 and Pt/SiO2, respectively. As a result, Pt/SiO2 exhibits considerably more reaction acceleration for the catalytic dehydrogenation of 2-propanol under microwave irradiation than Pt/Al2O3. We also find microwaves enhance the reduction of PtOx nanoparticles by using operando X-ray absorption near edge structure (XANES) spectroscopy. The present results indicate that significant local heating of platinum nanoparticles by microwaves is effective for the acceleration of catalytic reactions.

Development of a method for the synthesis of basic catalysts with high number of active species

Abstract Mesoporous silica MCF and metalosilicates Nb/MCF-14 and Ce/MCF-14 were modified with anchoring of melamine followed by (3-chloropropyl)trimethoxysilane functionalization. The texture/structure parameters, chemical composition and surface properties of synthesized samples were investigated by XRD, N2 adsorption/desorption, XPS, UV–vis, TG, elemental analysis and 2-propanol dehydration and dehydrogenation, whereas the activity of obtained catalysts was tested in the Knoevenagel condensation between benzaldehyde and malononitrile. The Knoevenagel reaction required the presence of basic active sites or a pair of acid-base active centers. The novelty of the presented work was the use of mesoporous cellular foam (MCF) also modified with niobium (Nb/MCF-14) or cerium species (Ce/MCF-14) as supports for melamine anchoring. The use of the mentioned supports allowed the investigation of the role of open structure of MCF and metal dopant on melamine loading, its stability and reactivity in the Knoevenagel condensation. The obtained results clearly demonstrate that cerium and niobium species loaded into MCF increase significantly the efficiency of melamine loading as well as its stability. The anchoring of melamine to silica and metalosilicates increase the activity of this modifier as a result of formation of secondary amine species. The presence of defected ceria in Mel/Ce/MCF-14 raises the basicity of anchored melamine due to the electron donating effect of ceria. Consequently, the amine species in melamine are more active in the Knoevenagel condensation than those in Mel/Nb/MCF-14 because niobium species do not change oxidation state as easily as defected ceria.

Birch-Type Reduction of Arenes in 2-Propanol Catalyzed by Zero-Valent Iron and Platinum on Carbon.

Catalytic arene reduction was effectively realized by heating in 2-propanol/water in the presence of Pt on carbon (Pt/C) and metallic Fe. 2-Propanol acted as a hydrogen source, obviating the need for flammable (and hence, dangerous and hard-to-handle) hydrogen gas, while metallic Fe acted as an essential co-catalyst to promote reduction. The chemical states of Pt and Fe in the reaction mixture were determined by X-ray absorption near-edge structure analysis, and the obtained results were used to suggest a plausible reaction mechanism, implying that catalytic reduction involved Pt- and Fe-mediated single-electron transfer and the dehydrogenation of 2-propanol.

Enhancement of Fixed-bed Flow Reactions under Microwave Irradiation by Local Heating at the Vicinal Contact Points of Catalyst Particles

The formation of local high temperature regions, or so-called “hot spots”, in heterogeneous reaction systems has been suggested as a critical factor in the enhancement of chemical reactions using microwave heating. In this paper, we report the generation of local high temperature regions between catalyst particles under microwave heating. First, we demonstrated that reaction rate of the dehydrogenation of 2-propanol over a magnetite catalyst was enhanced 17- (250 °C) to 38- (200 °C) fold when heated with microwave irradiation rather than an electrical furnace. Subsequently, the existence of microwave-generated specific local heating was demonstrated using a coupled simulation of the electromagnetic fields and heat transfer as well as in situ emission spectroscopy. Specific high-temperature regions were generated at the vicinal contact points of the catalyst particles due to the concentrated microwave electric field. We also directly observed local high temperature regions at the contact points of the particles during microwave heating of a model silicon carbide spherical material using in situ emission spectroscopy. We conclude that the generation of local heating at the contact points between the catalyst particles is a key factor for enhancing fixed-bed flow reactions under microwave irradiation.

Comparison of Stabilizer Effects on the Size, Dispersion, and Catalytic Property of Pt, PtCu, and PtRu Nanoparticles.

Carbon-supported Pt, Pt-Cu, and Pt-Ru nanoparticles were prepared by an alcohol reduction method in the presence of carboxylates and phosphinate in order to investigate the role of these stabilizers in the nanoparticle formation process and the effect on catalytic properties in 2-propanol oxidation. For the Pt-Cu system, long chain carboxylate gave small dispersed particles even with high metal loading while phosphinate gave aggregated particles. For the Pt and Pt-Ru systems, fewer aggregates were observed and the particle size was independent of the chain length of carboxylate while much smaller and dispersed particles were obtained with phosphinate. Phosphinate mainly prevents metal crystal growth while carboxylates prevent both crystal growth and formation of aggregated particles. Although surface poisoning is severe on small dispersed particles in 2-propanol oxidation, dehydrogenation of 2-propanol at low potential is little affected. Phosphinate-protected catalysts were more tolerant to poisoning promoting 2-propanol electrooxidation at high potential range. The presence of Cu promoted 2-propanol electrooxidation at low potential range. These components made phosphinate-protected PtCu best perform in 2-propanol oxidation at 30 °C.

ACETONE HYDRATION KINETICS AND EVALUATION OF INPUT OF 2-PROPANOL DEHYDRATION REACTION ON RANEY NICKEL UNDER HYDROGENATION CONDITIONS

The problem of kinetics of skeletal nickel samples saturation with hydrogen in an aqueous solution of 2-propanol of azeotropic composition was discussed. 2-propanol dehydrogenation and acetone hydrogenation rate constants were calculated. Kinetic model of processes under study was offered.

Catalytic Properties of Pure and K+-Doped CuO/MgO System Towards 2-Propanol Conversion

CuO/MgO system having different compositions was prepared by impregnation method followed by calcination at 400-900 °C. The effect of CuO content, calcination temperature and doping with small amounts of K+ species (1-3 mol %) on physicochemical, surface and catalytic properties of the system were investigated using XRD, adsorption of N2 at -196 °C, and conversion of isopropyl alcohol at 150-400 °C using a flow technique. The results revealed that the solids having the formulae 0.2 and 0.3 CuO/MgO calcined at 400 °C consisted of nanosized MgO and CuO as major phases together with Cu2O as minor phase. The BET-surface areas of different adsorbents are decreased by increasing CuO content, calcination temperature and K+- doping. MgO-support material showed very small catalytic activity in 2-propanol conversion. The investigated system behaved as selective catalyst for dehydrogenation of 2-propanol with selectivity > 80%. The catalytic activity increased by increasing CuO content and decreased by increasing the calcination temperature within 400-900 °C. K+ - doping increased the catalytic activity and catalytic durability.

Transfer hydrogenation over sodium-modified ceria: Enrichment of redox sites active for alcohol dehydrogenation

Ceria (CeO2) and sodium-modified ceria (Ce-Na) were prepared through combustion synthesis. Palladium was deposited onto the supports (Pd/CeO2 and Pd/Ce-Na) and their activity for the aqueous-phase transfer hydrogenation of phenol using 2-propanol under liquid flow conditions was studied. Pd/Ce-Na showed a marked increase (6×) in transfer hydrogenation activity over Pd/CeO2. Material characterization indicated that water-stable sodium species were not doped into the ceria lattice, but rather existed as subsurface carbonates. Modification of ceria by sodium provided more adsorption and redox active sites (i.e. defects) for 2-propanol dehydrogenation. This effect was an intrinsic property of the Ce-Na support and independent of Pd. The redox sites active for 2-propanol dehydrogenation were thermodynamically equivalent on both supports/catalysts. At high phenol concentrations, the reaction was limited by 2-propanol adsorption. Thus, the difference in catalytic activity was attributed to the different numbers of 2-propanol adsorption and redox active sites on each catalyst.

Efficient Visible Light-Driven Splitting of Alcohols into Hydrogen and Corresponding Carbonyl Compounds over a Ni-Modified CdS Photocatalyst.

Splitting of alcohols into hydrogen and corresponding carbonyl compounds has potential applications in hydrogen production and chemical industry. Herein, we report that a heterogeneous photocatalyst (Ni-modified CdS nanoparticles) could efficiently split alcohols into hydrogen and corresponding aldehydes or ketones in a stoichiometric manner under visible light irradiation. Optimized apparent quantum yields of 38%, 46%, and 48% were obtained at 447 nm for dehydrogenation of methanol, ethanol, and 2-propanol, respectively. In the case of dehydrogenation of 2-propanol, a turnover number of greater than 44 000 was achieved. To our knowledge, these are unprecedented values for photocatalytic splitting of liquid alcohols under visible light to date. Besides, the current catalyst system functions well with other aliphatic and aromatic alcohols, affording the corresponding carbonyl compounds with good to excellent conversion and outstanding selectivity. Moreover, mechanistic investigations suggest that an interface between Ni nanocrystal and CdS plays a key role in the reaction mechanism of the photocatalytic splitting of alcohol.

Catalytic activity of carbon nanotubes in the conversion of aliphatic alcohols

Carbon nanotubes (CNTs) obtained via the catalytic pyrolysis of hexane at 750°C were studied as the catalysts in conversion of C2–C4 alcohols. The efficiency of CNTs as catalysts in dehydration and dehydrogenation of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and tert-butanol was studied by means of pulse microcatalysis. The surface and structural characteristics of CNTs are investigated via SEM, TEM, DTA, BET, and XPS. CNTs are shown to be effective catalysts in the conversion of alcohols and do not require additional oxidative treatment. The regularities of the conversion of aliphatic alcohols, related to the properties of the CNTs surface and the structure of the alcohols are identified.

Electrocatalytic dehydrogenation of 2-propanol in electrochemical hydrogen pump reactor

There are few concerns on the hydrogen source except pure hydrogen and water for anode of electrochemical hydrogen pump (EHP) reactor. In this paper, the possibility of 2-propanol as the substitute of conventional hydrogen source was investigated. Dehydrogenation reaction conditions of 2-propanol were optimized, high performance of dehydrogenation could be obtained under 60°C with 1.0–2.0molL−1 2-propanol. Within 1.2V, the available current density of 2-propanol reaches 37.7mAcm−2, which could be equivalent to hundreds of bars hydrogen partial pressure in conventional three-phase hydrogenation reactor. When coupled with phenol hydrogenation in one EHP reactor, results indicate 2-propanol could be successfully performed as anode feed, and performance of phenol is almost as excellent as that in the phenol EHP reactors with hydrogen.