Butylphenyl-functionalized palladium nanoparticles as effective catalysts for the electrooxidation of formic acid

Monodisperse butylphenyl-functionalized palladium (Pd-BP, dia. 2.24 nm) nanoparticles were synthesized through co-reduction of butylphenyldiazonium and H(2)PdCl(4) by NaBH(4). Because of this unique surface functionalization and a high specific electro-chemical surface area (122 m(2) g(-1)), the Pd-BP nanoparticles exhibited a mass activity similar to 4.5 times that of commercial Pd black for HCOOH electrooxidation.National Science Foundation[CHE-0832605, CHE-1012258

Insights into nucleation and growth kinetics in seeded vacuum membrane distillation crystallization

A seeded vacuum membrane distillation crystallization (VMDC) process for treating magnesium sulfate solution was proposed. The permeate flux was investigated with respect to feed inlet temperature, vacuum pressure and feed velocity in order to determine operating conditions of VMDC. For the VMDC, the inlet and outlet temperatures of membrane distillation were maintained at 84 degrees C and 68 degrees C respectively, and the vacuum was 0.04-0.07 MPa. The nucleation and growth kinetics with the presence of seed in VMDC were investigated by comparison with the evaporation crystallization. Crystal nucleation and growth rates in evaporation crystallization and VMDC were both calculated using the population balance equation. It was found that the crystal growth rate in VMDC was slightly less than that in evaporation crystallization. Compared with evaporation crystallization, the secondary nucleation rate in VMDC was reduced due to the decrease of collision frequency between crystals

Parameter Estimation of Micro-Motion Targets for High-Resolution-Range Radar Using Online Measured Reference

Micro-motion dynamics produce Micro-range (m-R) signatures which are important features for target classification and recognition, provided that the range resolution of radar signal is high enough. However, dechirping the echo with reference measured by narrow bandwidth radar would generate the residual translational motion, which exhibits as random shifts of envelopes of range profiles. The residual translational motion would destroy the periodicity of m-R signatures and make a challenge to estimate rotational parameter. In this work, we proposed an efficient high-resolution range profile (HRRP)-based method to estimate rotational parameter, in which online measured reference distances are used to dechirp the radar raw echo. Firstly, the deduction for the modified first conditional comment of range profiles (MFCMRP) is introduced in detail, and the MFCMRP contain periodic and random components when dechirped by measured reference, corresponding to the rotational motion and the reference measured errors compared with actual reference. Secondly, the Wavelet Transform (WT) is utilized to separate the measured errors from the MFCMRP. The estimations of measured errors are used to compensate the MFCMRP, and then autocorrelation is performed on the estimated periodic component to obtain the estimation of rotational period. Lastly, the rotational amplitudes and phases are achieved by inverse Radon transform (IRT) of the compensated HRRP. The effectiveness of the proposed method in this paper is verified by synthetic data and measured radar data

Effect of impurity ions on the primary nucleation of ammonium alum precipitated from aqueous solution

Ammonium alum is an important powder material for producing high purity alumina. It is usually obtained by crystallization from aqueous solution, but impurity ions in solution have a great effect on the quality of final product particles. Effects of sodium, potassium and iron ions on the primary nucleation of ammonium alum were studied by measuring induction time and metastable zone width using focused beam reflectance measurement (FBRM). It was found that potassium ion or iron ion enhanced the nucleation, whereas sodium ion had no obvious effect. Analysis about the mechanism of impurity incorporation showed that, due to the isomorphous substitution, potassium ion or iron ion were easily incorporated into ammonium alum crystals. Moreover, potassium ion was more easily incorporated into crystal than iron ion. (C) 2020 Elsevier B.V. All rights reserved

Synthesis of Uniformly Spherical Bayerite from a Sodium Aluminate Solution Reacted with Sodium Bicarbonate

Bayerite was synthesized successfully by the precipitation reaction of a sodium aluminate solution with sodium bicarbonate in a mixed suspension mixed product removal (MSMPR) crystallizer. The particle size distribution of the prepared bayerite was significantly influenced by the temperature, the stirring speed, and the molar ratio (MR) of Na2Oc/Na2Ok as well as the addition rate of aqueous NaHCO3 solution in the system. The uniformly spherical bayerite with narrow "missing-fines-type" particle size distribution was obtained at 50 degrees C, with the MR of 0.66, at the agitation speed of 300 rpm in the MSMPR crystallizer. The synthesis of bayerite from the reactive NaAl(OH)(4)-NaHCO3 system was without an aging process. The thermal decomposition of the prepared bayerite was analyzed by TGA/DSC and XRD

Synthesis of calcium silicate as paper filler with desirable particle size from desilication solution of silicon-containing waste residues

Resource utilization of silicon is crucial to the sustainable reuse of the silicon-containing waste residues. In this study, a simple method to synthesize calcium silicate as paper filler with desirable particle size from the residues was proposed. Foil-shaped calcium silicate with the average particle size (APS) of about 10 mu m and the span of below 1.2 was successfully synthesized. Compared with larger calcium silicate, the obtained product used as paper filler could greatly improve the bulk of paper while maintaining similar tensile strength. The online focused beam reflectance measurement (FBRM) was used to investigate the hydration of CaO and the formation of calcium silicate. It was found that the hydration of CaO in NaOH solution with the presence of silicate played a key role in synthesizing the 10 mu m-sized calcium silicate. The formation of calcium silicate was speculated to be controlled by a liquid-liquid reaction. (C) 2020 Elsevier B.V. All rights reserved

Ind. Eng. Chem. Res.

The nucleation, growth, and agglomeration of monosodium aluminate hydrate (MAH) crystallization in concentrated sodium aluminate solutions were investigated in a steady-state mixed-suspension-mixed-product-removal (MSMPR) crystallizer, and the mechanism was analyzed in detail. The crystal growth was diffusion- and surface-integration-controlled, and the secondary nucleation, as a result of crystal-agitator and crystal-crystallizer collisions, was determined further. The agglomeration kernel, expressed in terms of mean residence time, growth rate, and suspension density, was found to have a positive order of about 0.52 in the suspension density, indicating that the agglomeration kernel increased at higher frequencies of collisions between particles. The growth rate of MAH was found to be higher than that of gibbsite in active NaAl(OH)(4)-NaHCO3 systems, but the nucleation rate of MAH was lower than that of gibbsite in seeded-hydrolysis processes.The nucleation, growth, and agglomeration of monosodium aluminate hydrate (MAH) crystallization in concentrated sodium aluminate solutions were investigated in a steady-state mixed-suspension-mixed-product-removal (MSMPR) crystallizer, and the mechanism was analyzed in detail. The crystal growth was diffusion- and surface-integration-controlled, and the secondary nucleation, as a result of crystal-agitator and crystal-crystallizer collisions, was determined further. The agglomeration kernel, expressed in terms of mean residence time, growth rate, and suspension density, was found to have a positive order of about 0.52 in the suspension density, indicating that the agglomeration kernel increased at higher frequencies of collisions between particles. The growth rate of MAH was found to be higher than that of gibbsite in active NaAl(OH)(4)-NaHCO3 systems, but the nucleation rate of MAH was lower than that of gibbsite in seeded-hydrolysis processes

Thermodynamics and nucleation mechanism of ammonium jarosite in sulfuric acid solution

Jarosite process is one of the most widely used methods in removing Fe, but in which the nucleation mechanism of ammonium jarosite has not been reported. Solubilities of the ammonium jarosite crystals under different Fe-2(SO4)(3) and (NH4)(2)SO4 concentrations and under different temperatures were measured, and the experiments of induction periods were systematically investigated in different temperatures (348 k, 358 k and 368 k) and H2SO4 concentrations (9 g/L, 10.8 g/L and 12.6 g/L) by reaction crystallization process based on the thermodynamic equilibrium data. According to the model of classical nucleation theory, the interfacial tension and the surface entropy factors in different conditions were calculated as 1.21 mJ/m(2), 1.85 mJ/m(2), 1.71 mJ/m(2) and 1.51, 1.27, 1.17. The SEM photographs of (H3O, NH4) Fe-3(SO4)(2)(OH)(6) approved that the ammonium jarosite crystals were clearly grown by the two-dimensional nucleation mechanism and/or the spiral growth mechanism. But the growth mechanism of (H3O, NH4)Fe-3(SO4)(2)(OH)(6) had been determined to be the continuous growth by the surface entropy factor. (C) 2017 Published by Elsevier B.V.</p

Precipitation of monosodium aluminate hydrate from concentrated sodium aluminate solution

Precipitation of monosodium aluminate hydrate (MAH) from concentrated sodium aluminate solution in the hydro-chemical process of alumina production was carried out in a continuously operated crystallizer. Crystal size distribution and morphology of MAH crystals were greatly influenced by parameters in the crystallization process, including mean residence time, supersaturation, temperature and agitation. Spherical MAH crystals with uniform size were successfully obtained. A condition of the mean residence time of 50 min, the temperature of 60 degrees C, the supersaturation of 5.3 and the agitation speed of 300 rpm was preferred in the precipitation of MAH crystals