2-propanol Dehydration Research Articles

Active site requirements for bio-alcohol dehydration: Effect of chemical structure and site proximity

Synthesis-structure-activity relations are reported, describing how interzeolite conversion (IZC) allows synthesis of ZSM-5 (MFI framework) with fixed physicochemical properties, except the variable local acid site (Al) arrangement, by variation of the synthesis time. Local confinement and acidity effects are probed by applying both H-ZSM-5 and Na-ZSM-5 samples in alcohol dehydration. Pyridine and divalent cobalt ion probing are used to quantify the amount of accessible acid sites and of Al in close proximity. Al in close proximity shows a strong influence on n-butanol dehydration turnover rates. The turnover rates are also strongly dependent on local confinement: in Na-form, ZSM-5 synthesized with more Al present as isolated species is a factor of 3–7 times more active than Na-ZSM-5 with fewer isolated Al. However if the zeolites are in proton form, ZSM-5 with more proximate sites show a higher activity compared to ZSM-5 with more isolated sites. Linear butene selectivity increases in Na-ZSM-5 compared to H-ZSM-5, caused by a suppressed dibutyl ether formation. The selectivity towards 1-butene is enhanced to a greater extent on proximate sites, likely due to a local/steric constraint at the active site. Decomposition of DBE over Na-ZSM-5 is more active compared to n-butanol dehydration, independent of acid site proximity. Also for 2-propanol dehydration, Na-ZSM-5 is less active than H-ZSM-5, yet the activity difference is attenuated compared to n-butanol dehydration. Essentially, due to the intrinsic higher reactivity of 2-propanol, the acid site requirement is less stringent. These findings highlight the importance of local confinement and Al proximity in acid-catalyzed conversion of oxygenated compounds.

Sulfured NiMo catalysts on TiO2-Nb2O5 nanocomposites for efficient hydrodesulfurization performance

The implementation of increasingly stringent environmental regulations has increased the demand for more active catalysts in hydrotreating. This study proposes the synthesis, characterization, and evaluation of bimetallic NiMo catalysts supported on TiO2-Nb2O5 nanocomposites for dibenzothiophene hydrodesulfurization. Samples containing 3, 5, and 10 wt% Nb2O5 were synthesized to examine the influence of Nb content on their catalytic activity and selectivity. Supports and oxidized catalysts were characterized using various techniques, including SEM-EDS, N2 physisorption, powder XRD, UV–vis DRS, Raman spectroscopy, and H2-TPR, while sulfured catalysts were further characterized by XPS and HRTEM. NiMo/TiNb3 and NiMo/TiNb5 catalysts displayed propene and diisopropyl ether as the main products in the 2-propanol dehydration reaction. A correlation was observed between hydrogenating capabilities in the HDS and dehydration tests with the Nb loading, suggesting that an optimal combination of Lewis/Brønsted acid sites enhances the BP/CHB ratio. All Nb-containing samples exhibited superior activity compared to their Nb-free counterparts, as indicated by the higher values of the pseudo-first-order rate constants (kHDS), which were higher for the NiMo/TiNb3 catalyst. These results were also associated with the respective textural characteristics, metal dispersion, and species distribution.

2-Propanol Dehydration on the Nodes of the Metal–Organic Framework UiO-66: Distinguishing Catalytic Sites for Formation of Propene and Di-isopropyl Ether

2-Propanol Dehydration on the Nodes of the Metal–Organic Framework UiO-66: Distinguishing Catalytic Sites for Formation of Propene and Di-isopropyl Ether

Catalytic dehydration of 2-propanol over nickel phosphide immobilized on natural bentonite

Catalytic dehydration of 2-propanol over nickel phosphide immobilized on natural bentonite

Performance of Modified Alumina-Supported Ruthenium Catalysts in the Reforming of Methane with CO2

Ruthenium (1 wt%) catalysts supported on alumina doped with alkaline (Na and K) and alkaline earth metals (Ba, Ca, and Mg) of different concentrations (1, 5, and 10 wt%) were tested in the dry reforming of methane. All catalysts were prepared by the successive impregnation method. Supports were characterized by X-ray diffraction, BET surface area, temperature-programmed desorption of CO2, and 2-propanol dehydration. Additionally, catalysts were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Stability tests to study coke deposition were performed using long-time dry reforming reactions. All the catalysts showed good catalytic activity, and activity falls were never detected. Ru metallic phase seemed to be resistant to coke formation even though its particles are sintered during a long-term reaction.

Determining the influence of microwave-induced thermal unevenness on vanadium oxide catalyst particles

• Thermal unevenness of V 2 O 5 catalyst due to microwaves was analyzed by thermography. • Local heat generation started from the contact point of spherical V 2 O 5 particles. • Thermal distribution dynamically changed depending on the oxidation state of V 2 O 5. • Raman spectra demonstrated the enhanced V 2 O 5 redox by microwaves. • Local hot spot and catalyst oxidation state synergistically accelerate catalytic reaction. Microwave (MW) heating accelerates various heterogeneous catalytic reactions at low temperatures, leading to energy-efficient catalytic processes. Herein we report the formation of MW–formed uneven thermal distribution at the interparticle of V 2 O 5 catalyst by using microscopic thermography and electromagnetic/thermal flow simulations. The local heat generation started from the contact point of the spherical catalyst particles. The uneven thermal distribution changed as the oxidation state of the catalyst dynamically changed during the dehydration of 2-propanol. In situ Raman spectroscopy suggested that dynamic change in the thermal gradient attributes to the oxidation state of the V 2 O 5 catalyst. As a result, the formation of the local hot spot at the contact point of the V 2 O 5 catalyst particles, as well as the oxidation state of V 2 O 5 due to MWs, synergistically affect the enhancement in the dehydration of 2-propanol. The present results provide important insights into a mechanistic understanding of the reaction enhancement of the fixed-bed flow reaction owing to the MW-induced uneven thermal distribution.

Effect of crystal size on the acidity of nanometric Y zeolite: number of sites, strength, acid nature, and dehydration of 2-propanol

Crystallinity damage in acid Y zeolite affects the direct relationship between the number of acid sites or conversion of 2-propanol and the zeolite size and the selectivity of 2-propene in nanosized Y zeolite.

Heteropolyacids supported on boron nitride and carbon nitride for catalytic and catalytic photo-assisted alcohol dehydration

Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O60 (P2W18) heteropolyacids (HPAs) are photo(catalysts) for various acid-promoted and redox catalytic reactions. Their activity increases if they are deposited on certain supports as metal oxides or carbon materials. Although the surface area and acid-base interactions of the HPAs with supports are considered as key factors for the performance of the binary material, the role of the local structure changes in the HPAs upon their immobilization on solids must be also of primary importance, directly affecting both acidity and photoredox properties. Here, the (photo)catalytic performance of Keggin and Wells-Dawson heteropolytungstates supported on boron nitride (BN) and two types of carbon nitride (C3N4) in the gas-solid 2-propanol dehydration to propene has been studied. Apart from characterizing the materials by a set of conventional laboratory-scale structural and physical-chemical techniques, an insight into the variations of the local structure of supported HPAs is provided by means of X-ray absorption spectroscopy (XAS), and their influence on the supported HPAs (photo)catalytic activity is discussed. The irradiation with UV light increased the activity of both heteropolytungstates with respect to the catalytic experiments. The apparent activation energy calculated for the photo-assisted process resulted always lower with respect to that obtained for the catalytic one alone. Moreover, the materials that showed the highest apparent turnover frequency (TOF) were those in which the HPAs were impregnated on graphitic C3N4 or on BN and, in particular, the highest TOF values were observed at the highest temperature for the PW12/BN and P2W18/BN samples. Interestingly, the highest activity of HPAs supported on BN seems to be due to the stabilization of the W octahedral coordination, according to the XAS data.

Real-Time Facile Detection of the WO3 Catalyst Oxidation State under Microwaves Using a Resonance Frequency.

Microwaves (MWs) are often used to enhance various heterogeneous catalytic reactions. Here, we demonstrate real-time monitoring of a catalyst’s oxidation state in a microwave catalytic reaction using a resonance frequency. The changes in the catalyst’s oxidation state during the reaction induced changes in the resonance frequency in the cavity resonator. The resonance frequency was not affected by 2-propanol adsorption, while the frequency decreased with the reduction of WO3 → WO3−x. That is, the redox state of the WO3 catalyst could be detected using the resonance frequency. The oxidation state of the WO3 catalyst was then directly observed by the resonance frequency during the dehydration reaction of 2-propanol by microwaves as a model reaction. Resonance frequency monitoring revealed that the enhanced dehydration of 2-propanol by microwaves was attributable to the reduction of the WO3 catalyst. Moreover, the temporal changes in the oxidation state of the WO3 catalyst detected by the resonance frequency coincided with that observed by operando Raman spectroscopy. Therefore, real-time resonance frequency monitoring allowed facile detection of the bulk catalyst oxidation state under microwaves without using any spectroscopic apparatus.

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.

Single-Facet Dominant Anatase TiO2 (101) and (001) Model Catalysts to Elucidate the Active Sites for Alkanol Dehydration

Alkanol dehydration on Lewis acid–base pairs of transition metal oxide catalysts is a reaction of importance in oxygen removal from biomass-derived feedstocks and their conversion to chemicals in general. However, catalysts with a high degree of structural heterogeneity, such as commercial TiO2 powders, are not well-suited to establish rigorous structure–function relationships at an atomic level. Here, we provide compelling evidence for the effects of surface orientation of TiO2 catalyst on elimination reactions of alcohols. Two anatase titania model catalysts, with preferential exposure of (101) and (001) facets, were synthesized and studied for 2-propanol dehydration using kinetic, isotopic, microscopic, and spectroscopic measurements, coupled with DFT calculations. Surface Lewis acid sites were found to be active for 2-propanol dehydration, and (101) facets are more reactive than (001) facets under the reaction conditions studied. On both anatase surfaces, 2-propanol was found to dehydrate via concerted E2 elimination pathways, but with different initial states and thus also different intrinsic activation barriers. Molecular 2-propanol dehydration dominates on TiO2 (101) while on TiO2 (001), 2-propanol simultaneously converts to more stable 2-propoxide before dehydration, which then requires higher activation energies for E2 elimination.

Keggin heteropolyacid supported on BN and C3N4: Comparison between catalytic and photocatalytic alcohol dehydration

The Keggin heteropolyacid (HPA), H3PW12O40 (PW12) has been supported on commercial boron nitride (BN) and two types of home prepared carbon nitride (C3N4). The supported PW12 was used in the gas-solid (photo)catalytic 2-propanol dehydration reaction to give propene at atmospheric pressure and temperatures in the range 70–120 °C and resulted more active than the pristine PW12. Reaction rate increased by increasing the temperature. Noticeably, the propene formation rate was higher by irradiating the catalytic system. The PW12/BN material resulted more active than PW12/C3N4. The acidity of the HPA cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction.

Morphology and reactivity of size-selected titanium oxide nanoclusters on Au(111).

The morphology and reactivity of mass-selected titania clusters, Ti3O6 and Ti3O5, deposited onto Au(111) were studied by scanning tunneling microscopy and temperature programmed desorption. Despite differing by only one oxygen atom, the stoichiometric Ti3O6 and the sub-stoichiometric ("reduced") Ti3O5 clusters exhibit very different structures and preferred binding sites. The Ti3O6 clusters bind at step edges and form small assemblies (2-4 clusters) on Au terraces, while the "reduced" Ti3O5 clusters form much larger fractal-like assemblies that can extend across step boundaries. Annealing the Ti3O5,6/Au(111) systems to higher temperatures causes changes in the size-distributions of cluster assemblies, but does not lead to the formation of TiOx nanoislands for temperatures ≤700 K. Reactivity studies show that the reduced Ti3O5 cluster has higher activity than Ti3O6 for 2-propanol dehydration, although both clusters exhibit substantial activity for dehydrogenation to acetone. Calculations using DFT+U suggest that the differences in aggregate morphology and reactivity are associated with the number of undercoordinated Ti3c sites in the supported clusters.

Operando Raman Spectroscopy of the Microwave-Enhanced Catalytic Dehydration of 2-Propanol by WO3

Operando Raman spectroscopy was performed to understand the mechanism of a microwave (MW)-enhanced fixed-bed catalytic reaction. An MW operando Raman spectroscopy system was constructed by integrating a Raman spectroscopy probe (785 nm) with a single-mode (TM110) MW cavity resonator equipped with a semiconductor MW generator. MW heating enhanced the dehydration of 2-propanol to diisopropyl ether and propylene by +54 to +60% under the air flow condition. In the argon flow condition, the conversion of 2-propanol was further enhanced by +71 to +83% with >99.9% selectivity toward propylene when MW heating was used. Operando Raman spectroscopy revealed that MW irradiation enhances the reduction of the WO3 surface and exhibits intense light emission, especially under the argon flow condition. The enhanced generation of WO3–x species on the surface of the WO3 catalyst should be, therefore, a key factor in the enhancement of the dehydration of 2-propanol under MW irradiation.

Ethylene Glycol as Entrainer in 1-Propanol Dehydration: Scrutiny of Physicochemical Properties of Ethylene Glycol+1-Propanol Binary Mixture at Different Temperatures

Density (ρ), and dielectric permittivity (ε) of the binary mixture of ethylene glycol + 1- propanol have been determined as a function of mole fraction of ethylene glycol at T = (298, 308 and 313)K. These measurements have been employed to compute thermodynamic properties like molar volume (V), and molar polarization (P) of the liquid mixtures. Excess properties such as VE, εE and PE for the binary mixture have also been calculated at different temperatures. In order to calculate the standard deviations of the excess properties, Redlich – Kister polynomial equation was used. The negative and positive values of the excess properties predicted the type and strength of molecular interactions between the components in the binary mixture.The excess molar volume for the mixture at all temperatures is found to be negative. The εE values for ethylene glycol + 1-propanol has been found to be negative at 298K and but positive values are obtained at 308 and 313K. The divergent magnitudes of εE values at different temperatures have been attributed to different strengths of hydrogen bond interactions as well as alignments of net dipoles.

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.

Surface reactivity of nanoporous carbons: preparation and physicochemical characterization of sulfonated activated carbon fibers

Here, we have examined the nanoporous activated carbon fibers (ACFs) sulfonated using the direct sulfonation and the staged method that included bromination, followed by sulfidation and oxidation. TEM confirmed the nanoporous structure of the prepared sulfonated ACFs. Nitrogen porometry and 2D nonlocal DFT simulations showed the nanoporosity reduction and variations of the pore size distribution because of the functionalization. Comparison of parameters of the SO3H groups confined in nanopores, e.g., the thermal stability and catalytic potential, showed that the most efficient acid sites, in the catalytic 2-propanol dehydration to propylene, are the SO3H groups grafted by the staged Houben–Weil methods. From the productivity of reactions used at the preparation stage, and in contrast to the one-staged aromatic substitution, the bromine addition to π sites of the edges of carbon matrix supplies enough active sites and is a reason for further high yields of the grafted thermostable SO3H groups. Hydrolysis of the grafted bromine and the surface oxidation of nanopores walls are parallel reactions that lowered the SO3H-related acidity, increasing the total acidity to 1.5 mmol g−1. The reported nanoporous sulfonated ACFs are effective to be used in the dehydration reactions catalyzed by solid acids.

Alcohols dehydration in heterogeneous system – FTIR method development for quantitative determination of catalytic parameters

Quantification of the FTIR spectra makes it possible to monitor in situ the catalytic reactions in heterogeneous systems using a batch-mode microreactor. The tested catalysts included a series of solid heteropolyacids (HPAs): H3PW12O40, H3PMo12O40, H6P2W18O62 and H6P2Mo18O62 with Keggin and Wells-Dawson anion structures. The FTIR has been used to monitor the reaction progress in the alcohol dehydrations, by in situ detection of changes in composition of the gas phase over the catalyst surface. This procedure made it possible to evaluate both the degree of conversion and the yields of products as a function of time and temperature. The studied reactions included dehydrations of methanol and of 2-propanol, both processes relying on the catalyst’s acidity. In both the reactions, the HPAs performance turned out to compare well with their acidity determinations carried out by measuring their heats of the NH3 sorption with the gas flow-through microcalorimetry. In case of the 2-propanol dehydration, the catalytic performance of the HPAs in this reaction has also been tested using a more typical setup of the flow-through mode microreactor, combined the gas chromatograph for down-stream detection, and the results have been compared to the batch-mode results for the process. A qualitative agreement between the two microreactor techniques has been found.

Catalytic efficiency of activated carbon functionalized with phosphorus-containing groups in 2-propanol dehydration

The functionalization of activated carbon (AC) by P-containing groups was conducted, and their thermal desorption was studied. Depending on the used method, the functionalized AC contains 0.5–1.45 mmol/g of acidic groups acting in catalytic 2-propanol dehydration. All catalysts showed 100% conversion of 2-propanol to propylene. The catalytic activity does not change with time under isothermal conditions and during their repeated use in catalysis, for 3 cycles of heating-cooling. In fact, the yield of propylene remains stable; it does not decrease with each cycle. Preliminary oxidation with nitric acid causes a small increase in the catalytic activity.

Catalytic Dehydration of 1-Propanol Over Silica Containing Sulfonic Acid Groups

Mesoporous silica with strongly acid sulfonic sites were synthesized and used as catalytic supports for catalytic dehydration of 1-propanol. This porous material with a large surface area and high porosity were prepared by a simplified sol-gel in an acidic medium and impregnated easily by -SO3H groups. The experimental results indicate that the very strong acidic sites contained on the surface are the seats of the reaction involving two molecules of n-propanol. By hydrogen bonding, ether compounds as well as the corresponding alkene are obtained in appreciable yield.