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In this study, 4A zeolite was prepared from opal waste rock by hydrothermal method and applied in ammonium ion adsorption. To optimize synthesis conditions, the effect of crystallization time (1–8 h), crystallization temperature (65–115°C), Na2O/SiO2 (0.6–2.0), H2O/Na2O (20–70), and SiO2/Al2O3 (1.0–3.5) was investigated. X-ray diffraction, scanning electron microscope imaging, cation exchange capacity, static water adsorption, Fourier transform infrared spectroscopy, and N2 adsorption–desorption isotherm were used for assessing properties of 4A zeolite. Adsorption experiments were performed by 1.0 g l−1 4A zeolite with NH4+ solution (5–300 mg l−1) for 4 h at room temperature. The experiment results revealed with a crystallization time of 3 h, a crystallization temperature of 85°C, Na2O/SiO2=1.0, H2O/Na2O = 40, and SiO2/Al2O3=2.0, the 4A zeolite synthesized had excellent performance with cation exchange capacity of 2.93 mmol (g dry zeolite)−1 and static water adsorption of 22.3%. The adsorption process was described by Freundlich model (R2>0.99) and the maximum adsorption capacity could reach to 53.11 mg g−1. The experimental results provided a novel approach for the utilization of opal waste rock, which is produced during the mining of opal-rich palygorskite, and for the synthesis of 4A zeolite and the removal of ammonium ion. [ABSTRACT FROM AUTHOR]

Dolomite–palygorskite (DP) composed of dolomite and palygorskite is a kind of special palygorskite. In this work, the phase, microstructure, and morphology of DP were characterized before and after calcination using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). Additionally, the process of thermal decomposition of DPC was determined by thermal gravity (TG) and differential thermal gravity (DTG) analysis and was compared with that of common dolomite. The results showed that the decomposition temperature of dolomite occurred in DPC started at 500 °C and ended at 780 °C, with a maximum peak at 745 °C. The decomposition temperature of dolomite in DPC was found to be 50 °C lower than that of common dolomite. Two reasons may explain this phenomenon. One involved the nano-effect of DPC caused by the nanoscale of dolomite in DPC and the special embedded structure between dolomite and palygorskite. The other was contributed to the reaction of carbonate with silicate enhancing the decomposition of dolomite in DPC. [ABSTRACT FROM AUTHOR]

Sedimentary palygorskite (SP) and hydrothermal palygorskite (HP) were characterized by XRF, TG/DSC, and XRD. The total iron and dissociative iron in palygorskite were detected using spectrophotometry. The results showed that about 3.57 wt% of FeO was detected in SP in contrast with 0.4 wt% in HP. SP was a Fe-substituted palygorskite, and HP was an Al-rich palygorskite. The occurrence of Fe substitution in SP resulted in two mass loss steps of coordinated water and resulted in a larger d spacing. The SP showed greater thermal stability than the HP. It was proposed the change of (200) diffraction peak and (240) diffraction peak reflect changes of tetrahedral and octahedral structures in palygorskite. [ABSTRACT FROM AUTHOR]

A series of palygorskite-supported manganese oxide (MnO x /PG) catalysts were prepared by a precipitation method using different manganese precursor. The as-prepared MnO x /PG catalysts were used to evaluate the catalytic oxidation of HCHO and characterized by BET, XRD, TG, Raman spectroscopy, TEM, H 2 -TPR, XPS, and chemical titration. The results showed that the crystalline phase, distribution and Mn valence states of MnO x on the surface of PG depended on the precursors. Birnessite-type manganese oxide (δ-MnO 2) formed and uniformly coated on the surface of PG when potassium permanganate (PP) was used as the precursor. The MnO x /PG-PP catalyst showed the best catalytic activity for HCHO removal at low temperature among these catalysts and achieved complete HCHO conversion at 150 °C. More importantly, the dynamic single-pass removal efficiency of MnO x /PG-PP catalyst for ppm-level HCHO oxidation was as high as 95% under high GHSV (300 L/g·h) at ambient temperature. MnO x /PG-PP catalyst also exhibited excellent cycling stability and long-term activity at low and ambient temperature. The kinetic results of MnO x /PG-PP catalyst showed that the oxidation of HCHO followed the Mars-van Krevelen mechanism. The possible reaction pathway of HCHO oxidation was proposed based on in situ DRIFTS and TPSR studies. The large specific surface area, highly distributed active component, a high proportion of Mn4+ species, and lattice oxygen content are responsible for the high catalytic activity of MnO x /PG-PP for oxidation of formaldehyde. This work developed a natural mineral supported manganese oxide as an inexpensive and efficient catalyst for the purification of HCHO in industrial or indoor air environment. Display Omitted • Crystalline phase of MnO x supported on the palygorskite depends on the precursor. • δ-MnO 2 uniformly coated on palygorskite (like a capsule) was synthesized. • δ-MnO x /PG showed excellent performance for HCHO removal at 25–150 °C. • The mechanism on HCHO removal over MnO x /PG was elucidated. [ABSTRACT FROM AUTHOR]

Abstract To availably utilize opal-palygorskite clay, dry beneficiation technique was applied to separate opal and palygorskite clay. Based on separated opal from opal-palygorskite clay, 4A zeolite was successfully synthesized by using a hydrothermal method. Box-Behnken was used to optimize Na 2 O/SiO 2 , H 2 O/Na 2 O and SiO 2 /Al 2 O 3 with cation exchange capacity (CEC) as the response value. The optimum parameters was determined to be Na 2 O/SiO 2 = 1.0, H 2 O/Na 2 O = 40, and SiO 2 /Al 2 O 3 = 2.0, and CEC got the maximum of 2.99 mmol/(g·dry zeolite) under the conditions. The as-obtained 4A zeolite was characterized by using X-ray diffraction (XRD), thermo gravimetric analysis (TG), acid-base titration, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and then was applied to remove Hg2+ from aqueous solution. The maximum removal capacity of Hg2+ was 41.99 mg/g and adsorption equilibrium was obtained with contact time of 2 h. Effects of pH, ionic strength, temperatures, metal cations, strippant kinds and cycle times on removal behaviors of Hg2+ onto 4A zeolite were investigated by batch experiments. The kinetics and isotherms of Hg2+ adsorption fitted well by pseudo-second kinetic and Langmuir models. When Hg2+-adsorbed 4A zeolite was desorbed using 1 mol/L NaNO 3 solution, the adsorption efficiency was maintained about 70% after four cycles. Highlights • Opal-palygorskite clay was separated by dry beneficiation technique. • 4A zeolite was synthesized successfully based on the separated opal. • The synthetic conditions of the 4A zeolite were optimized. • The performance of the 4A zeolite on removal of Hg2+ was evaluated. • The isotherms, kinetics, selectivity and effect of water chemistry were investigated. [ABSTRACT FROM AUTHOR]

The inexpensive and abundant material, palygorskite, was used as a promising catalyst support to prepare Fe-Ni/Pal catalysts. Catalytic steam reforming of toluene as a biomass tar model compound over these catalysts was investigated in a fixed-bed reactor under different parameters, including reaction temperatures and S/C molar ratios. The stability and lifetime of Fe 3 Ni 8 /Palygorskite catalyst was evaluated under optimal conditions and its kinetic parameters were determined as well. The fresh and used catalysts were characterized using X-ray diffraction (XRD), H 2 temperature-programmed reduction (H 2 -TPR), transmission electron microscopy (TEM), and Raman spectra. The results showed that the Fe 3 Ni 8 /Palygorskite catalyst with high dispersion was successfully prepared and exhibited superior catalytic performance compared with those of the monometallic catalysts (Fe 3 /Palygorskite and Ni 8 /Palygorskite) and the bare Palygorskite. Increasing the reaction temperature from 500 °C to 700 °C was beneficial for the toluene conversion and gaseous yields. The catalytic activity of Fe 3 Ni 8 /Palygorskite varied distinctly with the increase of S/C molar ratio and reached maximum at the the S/C molar ratio of 1.0. The apparent activation energy of 41.55 kJ mol −1 and the pre-exponential factor of 1.35 × 10 3  m 3  kg −1  h −1 were obtained for Fe 3 Ni 8 /Palygorskite in kinetic studies under optimal reaction conditions, respectively. The carbon deposition analysis of the used catalysts revealed that the formation of graphitic carbon rather than amorphous carbon was the main reason for the deactivation of Fe 3 Ni 8 /Palygorskite catalysts. When ceased the injection of steam into the reaction system, the graphitic carbon would be accelerating formed on the surface of the Fe 3 Ni 8 /Palygorskite and decreased its catalytic activity for toluene conversion. But owing to the water gas shift reaction, the catalytic activity of Fe 3 Ni 8 /Palygorskite seemed to recover gradually to its optimum. [ABSTRACT FROM AUTHOR]

Nano-scale Mn 1 − x Ce x O 2 catalysts supported on palygorskite (PG) with different dopant fractions were prepared by the co-precipitation method and applied in the catalytic oxidation of formaldehyde (HCHO). The obtained samples were characterized using BET, XRD, Raman spectroscopy, TEM, EDS, and H 2 -TPR to illustrate the physicochemical properties of the catalysts. After the introduction of cerium, the growth of manganese oxide was inhibited. However, an increase of the Ce/(Ce + Mn) ratio from 0.1 to 0.5 increased the particle size from 2.87 to 6.86 nm. A remarkable interface (grain boundaries) between MnO 2 and CeO 2 was observed, especially for low cerium molar fractions (0.1–0.4). The doping of cerium significantly enhanced the activity of manganese oxide for HCHO oxidation at 100–180 °C. The Mn 0.9 Ce 0.1 /PG catalyst exhibited the best activity, and HCHO was completely converted to CO 2 and H 2 O at 160 °C. The characterization results indicated that smaller particle size, surface-adsorbed oxygen species and abundant oxygen vacancies accounted for the high catalytic activity of the Mn 0.9 Ce 0.1 /PG catalyst for HCHO conversion. In addition, the Mn 0.9 Ce 0.1 /PG catalyst also displayed high stability in lifetime testing and excellent water-resistant performance. The experimental results suggest that palygorskite-supported Mn 0.9 Ce 0.1 is a promising catalyst for the catalytic oxidation of formaldehyde at low temperatures. [ABSTRACT FROM AUTHOR]

In this paper, the effect of calcination conditions on catalytic cracking of toluene over 3Fe8Ni/PG (PG: palygorskite) was investigated. The experimental parameters including the calcination temperature, time and atmosphere and reaction temperature were evaluated. The catalysts were characterized using X-ray diffraction (XRD), H 2 temperature-programmed reduction (TPR), transmission electron microcopy (TEM) and Raman spectroscopy. The gas composition was analyzed by a gas chromatograph (GC). The results showed that 3Fe8Ni/PG catalyst exhibited a higher catalytic reactivity for catalytic cracking of toluene than that of thermal cracking over quartz. In consideration of the thermal stability and catalytic reactivity of catalyst, a proper calcination temperature and time should be employed in the preparation of 3Fe8Ni/PG catalyst. The 3Fe8Ni/PG reduced in hydrogen at 700 °C for 2 h showed the highest catalytic reactivity as evidenced by the toluene conversion of 100% at the reaction temperature of 550 °C. The catalytic reactivity of 3Fe8Ni/PG reduced in hydrogen for toluene conversion was superior to that of 3Fe8Ni/PG calcinated in air, 3Fe/PG, and 8Ni/PG, which revealed that the awaruite (Ni Fe) was the active component for the decomposition of toluene. Moreover, steam reforming of toluene over 3Fe8Ni/PG catalysts suggested that 80% toluene conversion can be achieved and most of toluene was converted into H 2 and CO. Both amorphous carbon and graphitic carbon species were formed on 3Fe8Ni/PG catalysts after the catalytic reaction. The D/G ratio (the relative intensity of D-band to G-band ratio) was positively correlated to the catalytic reactivity of 3Fe8Ni/PG catalysts. [ABSTRACT FROM AUTHOR]

The adsorption of Eu(III) and U(VI) from aqueous solutions by palygorskite was studied by batch experiments under various experimental conditions. The palygorskite was characterized by TEM, XRD, FT-IR and potentiometric titration. The adsorption kinetics of Eu(III) and U(VI) on palygorskite were both well described by pseudo-second-order model with high correlation coefficient. The adsorption of Eu(III) and U(VI) by palygorskite decreased with increasing ionic strength, indicating outer-sphere surface complexation predominated. The adsorption isotherms indicated that the adsorption of Eu(III) and U(VI) by palygorskite fitted by Freundlich models were better than Langmuir models. The maximum adsorption capacities of Eu(III) and U(VI) on palygorskite calculated from Langmuir model were 24.26 and 46.75 mg·g − 1 at pH 4.0 and 333 K, respectively. The thermodynamic parameters suggested that the adsorption of Eu(III) and U(VI) on palygorskite was a spontaneous and endothermic process. [ABSTRACT FROM AUTHOR]

Dolomite–palygorskite clay (DPC) generally exists in palygorskite ore deposits. The morphological and mineralogical properties of a DPC sample were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM), and its performance on the removal of Cu(II) from an aqueous solution was evaluated by batch experiments. The effects of various parameters, viz., contact time (0–6 h), initial pH (2–6), initial Cu(II) concentration (50–300 mg L − 1 ), temperature (288–308 K), and ion strength ([Na + ]: 0.001–0.5 mol L − 1 ), on copper removal were investigated. The majority of copper ions were removed within an equilibrium time of 4 h, and kinetic data were expressed using a pseudo-second-order model. Maximum copper removal was achieved at pH 5 with a removal efficiency of 99.6%. The Freundlich model provided a better fit to equilibrium data, and the maximum removal capacity was estimated to be 225.7 mg g − 1 (308 K), which was nearly three times as high as that of dolomite (DO) and seven times that of palygorskite (PG). The thermodynamic results revealed the endothermic nature of the removal process and the strong chemical bonding between Cu(II) and DPC. Ion strength studies and TEM analyses indicated that the major mechanisms for removal of Cu(II) by DPC were surface precipitation and dissolution reactions by the formation of basic copper carbonate [CuCO 3 ·Cu(OH) 2 ], surface complexation, and electrostatic attraction. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have prepared palygorskite-supported Fe and Ni catalysts. [•] Catalytic cracking of rape straw is used to reduce tar content in biomass gasification gas. [•] Combustible gas derived from the pyrolysis increased with an increase in gasification temperature. [ABSTRACT FROM AUTHOR]

Catalytic decomposition is a very attractive way to convert tar components into H2, CO and other useful chemicals. The performance of Fe3Ni8/PG (palygorskite, PG) reduced in hydrogen at different temperatures for the catalytic decomposition of benzene has been assessed. Benzene was used as the model biomass tar. The effects of calcination atmosphere, temperatures and benzene concentration on catalytic cracking of benzene were measured. The results of XRD (X-Ray Diffraction), TEM (Transmission Electron Microscope), TPR (Temperature Program Reduction), TPSR (Temperature Program Surface Reduction), TC (Total Carbon), the reactivity component and reaction mechanism over Fe3Ni8/PG for catalytic cracking of benzene are discussed. The results showed particles of awaruite (Fe, Ni) about 2–30nm were found on the surface of palygorskite by TEM when the calcination temperature was 600°C. Particles with size smaller than 30nm were obtained on all prepared Fe3Ni8/PG catalysts as shown by XRD. The nanoparticles proved to be the reactive component for catalytic cracking of benzene and the increase of active particle size caused the decrease in the reactivity of Fe3Ni8/PG. Fe3Ni8/PG annealed in hydrogen at 600°C was proved to have the best reactivity in experiments (45% hydrogen yield). High concentration benzene (448g/m3) accelerated the formation of carbon deposition. However, iron oxide decreases carbon deposition and increases the stability of catalyst for catalytic cracking of benzene. The application of Fe3Ni8/PG catalysts was proved a very effective catalyst for the catalytic cracking of benzene. [ABSTRACT FROM AUTHOR]

Abstract: Palygorskite has a fibrous like morphology with a distinctive layered appearance. The simplified formula of palygorskite (Mg5Si8O20(OH)2(OH2)4⋅nH2O) indicates that two different types of water are present. The dehydration and rehydration of palygorskite have been studied using thermogravimetry and H2O-temperature programmed desorption. X-ray diffractograms, NH3 adsorption profiles, and NH3 desorption profiles were obtained for thermally treated palygorskite as a function of temperature. The results proved water molecules were mainly derived from Si–OH units. In addition, five kinds of acid sites were found for palygorskite. The number of acid sites of external surfaces was larger than that of the internal surfaces. Bonding on the internal surface acid sites was stronger than the bonding of the external surfaces. Rehydration restored the folded structure of palygorskite when thermal treatment temperature was lower than 300°C. [Copyright &y& Elsevier]

The Al-promoted Ni-based catalysts were prepared by co-precipitation method using natural clay mineral-palygorskite (Pal) as the support. The physicochemical properties of the catalysts were studied by XRD, BET, H 2 -TPR, TEM, XPS and Raman spectroscopy. The catalytic performances of the catalysts for CO 2 reforming of methane (DRM) were investigated under different parameters including Al content, reaction temperatures, CH 4 concentration and gas hourly space velocity (GHSV), and the long-term stability was also evaluated. The results showed that the addition of Al apparently favored the catalytic activity and stability of the catalysts for DRM reactions. The Ni/Pal catalyst with Al content of 8% (Ni 8 /Al 8 /Pal) exhibited the best activity for DRM at 700 °C in terms of the CH 4 and CO 2 conversions, which was related to the high dispersion and small crystal sizes of Ni particles. The variations of CH 4 concentration and GHSV showed little effect on the catalytic activity of Ni 8 /Al 8 /Pal for CH 4 conversion. Long-term stability (140 h) and H 2 /CO molar ratio of roughly 0.98 can be achieved. The carbon deposition of the spent catalysts indicated that mainly graphite-type carbon deposition was formed on the surface of the catalysts when Al content was lower than 8%; however, most of the carbon deposition was removed over the Ni 8 /Al 8 /Pal and Ni 8 /Al 15 /Pal catalysts. • The Al-promoted Ni-based catalysts were prepared by co-precipitation method using palygorskite (Pal) as the support. • The strong interactions of Ni with Al 2 O 3 and Pal was observed over the Al-promoted Ni/Pal catalysts. • The Ni 8 /Al 8 /Pal exhibited the best activity for DRM due to the high dispersion and small particle sizes of Ni. • The resistance to carbon deposition was highly enhanced after the addition of Al to the Ni/Pal system. [ABSTRACT FROM AUTHOR]

Achieving low-level formaldehyde (HCHO) catalytic oxidation at ambient temperature under a high gas-hourly space velocity (GHSV) remains challenging. In this study, MnO 2 -based catalysts were prepared via a facile in-situ redox reaction using palygorskite (PG), montmorillonite (MT) and diatomite (DT) as support materials. The results indicated that these minerals substantially enhanced the performance of HCHO oxidation compared with that of commercial Al 2 O 3 at ambient temperature. The as-prepared MnO 2 /PG exhibited the superior catalytic performance, where 100% removal efficiency of 1 ppm HCHO in 1500 min remained under a GHSV of 150,000 h−1. The performance order of the as-prepared catalysts at 1500 min was MnO 2 /PG (100%) > MnO 2 /MT (87%) > MnO 2 /DT (74%) > MnO 2 /Al 2 O 3 (59%). More importantly, the MnO 2 /PG catalyst exhibited the highest CO 2 selectivity (72.1%) and excellent long-term stability after five cycles. The kinetic results for HCHO oxidation followed the second-order kinetics. The well-distributed MnO 2 , abundant hydroxyl species, and Mn3+ and Mn4+ couples were responsible for the excellent catalytic performance of MnO 2 /PG. In addition, the incorporation of MnO 2 with PG increased the electron density of the MnO 2 /PG surface, which was also related to the excellent performance for HCHO oxidation. A possible reaction mechanism for HCHO oxidation was proposed based on XPS, in-situ DRIFTS and electrochemical analyses. This study paves a road for the development of MnO 2 /mineral hybrid catalysts for indoor air purification at ambient temperature. Unlabelled Image • Mineral-supported MnO 2 catalysts was prepared by facile in-situ redox reaction method. • Mineral supports enhanced the performance of MnO 2 -based catalysts for HCHO oxidation. • The surface hydroxyls of mineral supports favored the adsorption of HCHO • Palygorskite as the support showed superior HCHO oxidation activity compared with other minerals. [ABSTRACT FROM AUTHOR]