Active surface centres in vanadium pentoxide/alkali metal sulphate heterogeneous catalysts for 2-propanol decomposition

1979 ◽  
Vol 57 (18) ◽  
pp. 2464-2469 ◽  
Author(s):  
David Victor Fikis ◽  
William John Murphy ◽  
Robert Anderson Ross
Keyword(s):  
Alkali Metal ◽  
Surface Area ◽  
Vanadium Pentoxide ◽  
Heterogeneous Catalysts ◽  
Catalyst Activity ◽  
Active Surface ◽  
Hydroxyl Groups ◽  
Kinetic Measurements ◽  
The Stability ◽  
The Individual

Infrared spectra of the surfaces of vanadium pentoxide and vanadium pentoxide containing 9.09 mol% caesium and potassium, as sulphates, have been determined after exposure to 2-propanol for various times. Interpretation of the spectra leads to the proposal that the principal source of catalyst activity may be associated with surface hydrogen and hydroxyl groups on V5+ and V4+ sites. The "stability" of the catalysts towards reduction by the alcohol was consistent with the activity series derived from kinetic measurements: V2O5 (pure) < V2O5 (Cs) < V2O5 (K). The degree of sample reduction has also been assessed qualitatively by measurements of the ratio of surface area before to that after reaction and the same catalyst sequence was established. The trend in surface area ratios was similar to that shown by the surface "Tammann" temperatures of vanadium pentoxide and alkali metal sulphates which has been taken to imply that the ease and (or) extent with which the sulphates enter into inter-solid reactions with the oxide in the preparation stage may exert influence on the subsequent reducibility of the individual members of the catalyst series.

scholarly journals Bonding in Group 1 Citrate Salts

2014 ◽  
Vol 70 (a1) ◽  
pp. C655-C655
Author(s):  
James Kaduk ◽  
Alagappa Rammohan
Keyword(s):  
Hydrogen Bonds ◽  
Alkali Metal ◽  
Weak Interactions ◽  
Alkali Metal Cation ◽  
Quantitative Measure ◽  
Electrostatic Energy ◽  
Hydroxyl Groups ◽  
Local Environments ◽  
The Stability ◽  
Cation Size

Computational studies of > 15 new crystal structures and the 10 previously-reported structures of alkali metal citrates provide insight into why the atoms are where they are. The metal-citrate bonding is predominantly ionic, with very little covalent character, which decreases as the cation size increases. Bond valence calculations indicate that most cations are crowded, and that the crowding decreases as the cation size increases. Although most oxygen atoms coordinate to the metals, a few do not, and they tend to be the least-negative oxygens. Both the citrate hydroxyl groups and water molecules tend to bridge two cations, and the carboxylate coordination is more varied. The solid state energy differences are dominated by differences in van der Waals and electrostatic energy contributions. In the Li and Na salts, the citrate anion occurs predominantly in a higher-energy "kinked" conformation, rather than the extended lowest-energy conformation observed in salts of the larger cations. Detailed conformational analysis of the citrate anions enables quantification of the conformational energy costs in these solids. Hydrogen bonding is important to the stability of these salts. The Mulliken overlap population in the hydrogen bonds provides a quantitative measure of their strength, and permits identification of long (weak) interactions which are significant in some of these compounds. Patterns in both the local environments of the hydrogen bonds and the more-extended features (graph sets) are noted. Polymorphs and sets of isostructural compounds permit more-detailed analysis of the structures and energetics in these compounds. The order of ionization of the three carboxylic acid groups is in general central/terminal/terminal, but there are two exceptions. While we have concentrated on salts containing a single alkali metal cation (and hydrogen), the structures of NaK2C6H5O7 and NaKHC6H5O7 provide an exciting window on a larger universe of mixed salts.

Magnetic Spinel Ferrite: An Efficient, Reusable Nano Catalyst for HMFSynthesis

2021 ◽  
Vol 10 ◽  
Author(s):  
Jyoti Dhariwal ◽  
Ravina Yadav ◽  
Sheetal Yadav ◽  
Anshu Kumar Sinha ◽  
Chandra Mohan Srivastava ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Heterogeneous Catalysts ◽  
Spinel Ferrite ◽  
Active Surface ◽  
Catalytic Performance ◽  
Ferrite Nanoparticles ◽  
Precipitation Method ◽  
Magnetic Characteristics ◽  
Nano Catalyst

Aim: In the present work, the preparation and catalytic activity of spinel ferrite [MFe2O4; M = Fe, Mn, Co, Cu, Ni] nanoparticles to synthesize 5-hydroxymethylfurfural (HMF) have been discussed. Background: Ferrites possess unique physicochemical properties, including excellent magnetic characteristics, high specific surface area, active surface sites, high chemical stability, tunable shape and size, and easy functionalization. These properties make them essential heterogeneous catalysts in many organic reactions. Objective: This study aims to synthesize a series of transition metal ferrite nanoparticles and use them in the dehydration of carbohydrates for 5-hydroxymethylfurfural (HMF) synthesis. Method: The ferrite nanoparticles were prepared via the co-precipitation method, and PXRD confirmed their phase stability. The surface area and the crystallite size of the nanoparticles were calculated using BET and PXRD, respectively. Result: The easily prepared heterogeneous nanocatalyst showed a significant catalytic performance, and among all spinel ferrites, CuFe2O4 revealed maximum catalytic ability. Conclusion: Being a heterogeneous catalyst and magnetic in nature, ferrite nanoparticles were easily recovered by using an external magnet and reused up to several runs without substantial loss in catalytic activity. Others: HMF was synthesized from fructose in a good yield of 71%.

scholarly journals Characterization of Modified and Polymer Coated Alumina Surfaces by Infrared Spectroscopy

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Ashraf Yehia El-Naggar
Keyword(s):  
Infrared Spectroscopy ◽  
Alkali Metal ◽  
Ftir Spectroscopy ◽  
Surface Properties ◽  
Adsorption Properties ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Structure Changes ◽  
The Individual

The prepared, modified, and coated alumina surfaces were characterized by infrared spectroscopy (FTIR) to investigate the surface properties of the individual and double modified samples. FTIR helps in reporting the changes occurred in hydroxyl groups as well as the structure changes as a result of thermal treating, hydrothermal treating, silylation treating, alkali metal treating, coating, and bonding with polymer. FTIR spectroscopy represents the strength and abundance of surface acidic OH which determine the adsorption properties of polar and nonpolar sorbents. Generally, all treated samples exhibit decrease of OH groups compared with those of parent ones producing alumina surfaces of different adsorptive powers.

Contribution to the thermodynamics of complexes of alkali metal cations with dibenzo-18-crown-6 in water-nitrobenzene extraction system

1984 ◽  
Vol 49 (1) ◽  
pp. 39-44 ◽  
Author(s):  
Emanuel Makrlík ◽  
Jaroslava Hálová ◽  
Miroslav Kyrš
Keyword(s):  
Alkali Metal ◽  
Alkali Metal Cation ◽  
Alkali Metal Cations ◽  
Complex Species ◽  
Cation Order ◽  
Extraction Constants ◽  
Equilibrium Data ◽  
Individual Extraction Constants ◽  
The Stability ◽  
The Individual

The stability constants for the ML+ complex species, where M+ is an alkali metal cation and L is dibenzo-18-crown-6, in nitrobenzene saturated with water were calculated by employing published equilibrium data. The stability is found to increase in the cation order Li+ < Cs+ < Rb+ < K+ < Na+. For the NaL+, KL+, RbL+, and CsL+ complex cations the individual extraction constants in the water-nitrobenzene system were determined; their values increase in the series Na+ < K+ < Rb+ < Cs+.

scholarly journals Catalysis of Methanol-Air Mixture Using Platinum Nanoparticles for Microscale Combustion

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
James R. Applegate ◽  
Howard Pearlman ◽  
Smitesh D. Bakrania
Keyword(s):  
Surface Area ◽  
Platinum Nanoparticles ◽  
Flow Reactor ◽  
Catalyst Activity ◽  
High Surface ◽  
High Surface Area ◽  
Catalyst Loading ◽  
Bulk Temperature ◽  
Flow Parameters ◽  
The Stability

High surface area, active catalysts containing dispersed catalytic platinum nanoparticles (dp∼11.6 nm) on a cordierite substrate were fabricated and characterized using TEM, XRD, and SEM. The catalyst activity was evaluated for methanol oxidation. Experimental results were obtained in a miniature-scale continuous flow reactor. Subsequent studies on the effect of catalyst loading and reactor flow parameters are reported. Repeat tests were performed to assess the stability of the catalyst and the extent of deactivation, if any, that occurred due to restructuring and sintering of the particles. SEM characterization studies performed on the postreaction catalysts following repeat tests at reasonably high operating temperatures (∼500°C corresponding to ∼0.3Tmfor bulk platinum) showed evidence of sintering, yet the associated loss of surface area had minimal effect on the overall catalyst activity, as determined from bulk temperature measurements. The potential application of this work for improving catalytic devices including microscale reactors is also briefly discussed.

Preparation and characterisation of vanadium pentoxide supported rhodium catalyst

1988 ◽  
Vol 46 ◽  
pp. 946-947
Author(s):  
A. Legrouri
Keyword(s):  
Aqueous Solution ◽  
Thermal Decomposition ◽  
Physicochemical Properties ◽  
Surface Area ◽  
Vanadium Pentoxide ◽  
High Purity ◽  
Gas Adsorption ◽  
Rhodium Catalyst ◽  
Optical Methods ◽  
Reducible Oxides

The industrial importance of metal catalysts supported on reducible oxides has stimulated considerable interest during the last few years. This presentation reports on the study of the physicochemical properties of metallic rhodium supported on vanadium pentoxide (Rh/V2O5). Electron optical methods, in conjunction with other techniques, were used to characterise the catalyst before its use in the hydrogenolysis of butane; a reaction for which Rh metal is known to be among the most active catalysts.V2O5 powder was prepared by thermal decomposition of high purity ammonium metavanadate in air at 400 °C for 2 hours. Previous studies of the microstructure of this compound, by HREM, SEM and gas adsorption, showed it to be non— porous with a very low surface area of 6m2/g3. The metal loading of the catalyst used was lwt%Rh on V2Q5. It was prepared by wet impregnating the support with an aqueous solution of RhCI3.3H2O.

Implications of Person Fluctuation for the Stability and Validity of Test Scores

Methodology ◽  
2006 ◽  
Vol 2 (4) ◽  
pp. 142-148 ◽  
Author(s):  
Pere J. Ferrando
Keyword(s):  
Item Response ◽  
Test Scores ◽  
Temporal Stability ◽  
Person Fit ◽  
Item Parameters ◽  
Individual Trait ◽  
The Stability ◽  
The Individual ◽  
Different Levels ◽  
Fluctuation Model

In the IRT person-fluctuation model, the individual trait levels fluctuate within a single test administration whereas the items have fixed locations. This article studies the relations between the person and item parameters of this model and two central properties of item and test scores: temporal stability and external validity. For temporal stability, formulas are derived for predicting and interpreting item response changes in a test-retest situation on the basis of the individual fluctuations. As for validity, formulas are derived for obtaining disattenuated estimates and for predicting changes in validity in groups with different levels of fluctuation. These latter formulas are related to previous research in the person-fit domain. The results obtained and the relations discussed are illustrated with an empirical example.

Tenacious Mass Transfer Limitations Drive Catalytic Selectivity during Electrochemical Carbon Dioxide Reduction

2019 ◽  
Author(s):  
Kailun Yang ◽  
Recep Kas ◽  
Wilson A. Smith
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Catalyst Layer ◽  
Active Surface ◽  
Active Surface Area ◽  
High Concentration ◽  
Copper Electrodes ◽  
Surface Enhanced ◽  
Local Current

<p>This study evaluated the performance of the commonly used strong buffer electrolytes, i.e. phosphate buffers, during CO<sub>2</sub> electroreduction in neutral pH conditions by using in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Unfortunately, the buffers break down a lot faster than anticipated which has serious implications on many studies in the literature such as selectivity and kinetic analysis of the electrocatalysts. Increasing electrolyte concentration, surprisingly, did not extend the potential window of the phosphate buffers due to dramatic increase in hydrogen evolution reaction. Even high concentration phosphate buffers (1 M) break down within the potentials (-1 V vs RHE) where hydrocarbons are formed on copper electrodes. We have extended the discussion to high surface area electrodes by evaluating electrodes composed of copper nanowires. We would like highlight that it is not possible to cope with high local current densities on these high surface area electrodes by using high buffer capacity solutions and the CO<sub>2</sub> electrocatalysts are needed to be evaluated by casting thin nanoparticle films onto inert substrates as commonly employed in fuel cell reactions and up to now scarcely employed in CO<sub>2</sub> electroreduction. In addition, we underscore that normalization of the electrocatalytic activity to the electrochemical active surface area is not the ultimate solution due to concentration gradient along the catalyst layer.This will “underestimate” the activity of high surface electrocatalyst and the degree of underestimation will depend on the thickness, porosity and morphology of the catalyst layer. </p> <p> </p>

The role of secondary alcoholic groups of D-galacturonan in its degradation with exo-D-galacturonanase

1980 ◽  
Vol 45 (2) ◽  
pp. 427-434 ◽  
Author(s):  
Kveta Heinrichová ◽  
Rudolf Kohn
Keyword(s):  
Acetyl Derivative ◽  
Competitive Inhibitor ◽  
Hydroxyl Groups ◽  
Pectic Acid ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
The Individual ◽  
Degradation Degree ◽  
Derivatives Of

The effect of exo-D-galacturonanase from carrot on O-acetyl derivatives of pectic acid of variousacetylation degree was studied. Substitution of hydroxyl groups at C(2) and C(3) of D-galactopyranuronic acid units influences the initial rate of degradation, degree of degradation and its maximum rate, the differences being found also in the time of limit degradations of the individual O-acetyl derivatives. Value of the apparent Michaelis constant increases with increase of substitution and value of Vmax changes. O-Acetyl derivatives act as a competitive inhibitor of degradation of D-galacturonan. The extent of the inhibition effect depends on the degree of substitution. The only product of enzymic reaction is D-galactopyranuronic acid, what indicates that no degradation of the terminal substituted unit of O-acetyl derivative of pectic acid takes place. Substitution of hydroxyl groups influences the affinity of the enzyme towards the modified substrate. The results let us presume that hydroxyl groups at C(2) and C(3) of galacturonic unit of pectic acid are essential for formation of the enzyme-substrate complex.

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