Al Species Research Articles

Influence of extra-framework Al in Fe-MOR catalysts for the direct conversion of methane to oxygenates by nitrous oxide

Iron-containing zeolites play an important role in the selective oxidation of methane to oxygenates by nitrous oxide. A solid-state ion exchange method is adopted to prepare Fe-MOR zeolite catalysts with different amounts of extra-framework Al. EPR spectra and UV–vis spectra show that the percentage of iron ions in tetrahedral or octahedral coordination increases while those of clustered Fe species decrease by the addition of extra-framework Al species. Nitrous oxide titration reveals that more active Fe centers are formed, which promote the nitrous oxide consumption. The number of active centers in the catalyst with the introduction of extra-framework Al is about four times that of the catalyst without the addition of extra-framework Al. Due to this, there is an increase in the methane conversion, total selectivity and yield of oxygenates.

Hierarchical hollow manganese-magnesium-aluminum ternary metal oxide for fluoride elimination

Rational designs and syntheses for advanced structures are of immense importance to enhance adsorption performances toward a variety of materials. In this study, the synthesis of a novel hierarchical hollow manganese-magnesium-aluminum ternary metal oxide (MMA) via a green hydrothermal strategy coupled with a calcination process serves as a robust adsorbent for fluoride elimination. Combining the strong affinities Mn, Mg, and Al species have toward fluoride into a 3D-hierarchical hollow structure with an adequately accessible adsorption surface can remarkably boost the migration and diffusion of fluoride and provide more mass diffusion pathways for fluoride elimination. Remarkably, the adsorption process follows the pseudo-second-order model and the Langmuir isotherm model with a considerable performance of 63.05 mg/g. Moreover, the adsorbent retained outstanding selectivity and recyclability. Overall, the results from the universal characterization techniques and batch experiments validate that the potential adsorption mechanisms were electrostatic attraction and ion exchange, and complexation. As such, the present method expands the current adsorbent toolbox by providing a rational design and synthesis of a highly efficient adsorbent material for use in managing environmental pollution.

Organic and Inorganic Matter Removal Using High Polymeric Al13 Containing Polyaluminium Chloride

The ability of locally laboratory-synthesized polyaluminium chloride (PAC) with high Al13 content (PAC-Al13) to remove organic, inorganic matter and colour from potable water, agricultural and electroplating wastewaters was evaluated relative to commercial PAC (PACI). PAC-Al13 used in this study was prepared using batch titration of NaOH into AlCl3·6H2O solution under vigorous stirring as opposed to the conventional slow-base titration method. The highly pure PAC-Al13 (containing 79% polymeric Al13 species) with high basicity (87%) was isolated and extracted using the sulphate displacement method and metathesis reaction. PAC-Al13 showed higher COD (85–96%), metals (95–100%), TDS (86–90%) and colour (90–95%) removal compared with PACI, i.e. COD (57–74%), metals (71–99%), TDS (58–80%) and colour (85–92%). The dominance of polymeric Al13 species in PAC-Al13 was supported from the scanning electron microscopy images (presence of Keggin structure of Al13) and the 27Al nuclear magnetic resonance analysis that showed the appearance of a single peak at 62.1 ppm. This study demonstrated the potential of using a new type of PAC, produced using simple preparation technique and contain high polymeric Al13 species, that has the ability to remove contaminants from water and wastewater systems more efficiently.

Rates of levoglucosanol hydrogenolysis over Brønsted and Lewis acid sites on platinum silica-alumina catalysts synthesized by atomic layer deposition

Nanoscale coatings of AlOx were deposited onto SiO2 using atomic layer deposition (ALD) to synthesize amorphous silica-alumina (SiAl) catalysts, and these catalysts were investigated for levoglucosanol (Lgol) hydrogenolysis. With decreasing Al2O3 loading, the ratio of Brønsted to Lewis acid sites, measured by NH3-TPD and pyridine-FTIR, systematically increases, while the Al coordination, measured by solid state 27Al NMR, decreases. These structural changes correspond to an increasing mass-normalized rate of Lgol hydrogenolysis. We model the mass-normalized reaction rate as the sum of independent contributions from Brønsted and Lewis sites, showing that Brønsted acid sites on ALD-AlOx/SiO2 catalysts have a 6-times higher turnover frequency (TOF) than Lewis acid sites on these catalysts. Additionally, Lewis acid sites on ALD-AlOx/SiO2 catalysts (potentially related to Al(V) species) have a 4-times higher TOF than Lewis acid sites on bulk γ-Al2O3. The overall mass-normalized reactivity of ALD-AlOx/SiO2 catalysts is due to Lewis acid sites at the highest Al2O3 loading, while it is predominantly due to Brønsted acid sites at the lowest Al2O3 loadings. This work provides a new approach to synthesize amorphous SiAls with tunable Brønsted/Lewis acid site ratio and reveals differences in the reactivity of Brønsted and Lewis acid sites on these materials.

Effects of crop straw biochars on aluminum species in soil solution as related with the growth and yield of canola (Brassica napus L.) in an acidic Ultisol under field condition.

The toxicity of aluminum (Al) to plants in acidic soils depends on the Al species in soil solution. The effects of crop straw biochars on Al species in the soil solution, and canola growth and yield were investigated in this study. In a long-term field experiment, there were four treatments, which were a control, rice straw biochar (RSB), canola straw biochar (CSB), and peanut straw biochar (PSB). The soil solution was collected in situ, the Al species were identified, and the relationships between the concentration of phytotoxic Al and canola growth and yield were evaluated. The results showed that applying the three biochars resulted in significant decreases in the concentrations of total Al, monomeric Al, and monomeric inorganic Al (P < 0.05). The Al3+, Al-OH, and Al-SO4 proportions of the total Al also decreased. The abilities of the different biochars to reduce dissolved Al followed the order PSB > CSB > RSB, which was consistent with the alkalinity of these biochars. Application of the biochars significantly decreased the concentration of phytotoxic Al (Al3+ + Al-OH), which improved canola growth and increased the canola seed and straw yields. Plant height, leaf number per plant, area per leaf, chlorophyll content, and canola yield were negatively correlated with the Al3+ + Al-OH concentrations. Therefore, the results showed that crop straw biochars can be used to ameliorate soil acidity and alleviate Al toxicity in acidic soils, and that peanut straw biochar is the best amendment for acidic soils.

Ultrafine Ru species within confined space: An efficient adsorbent for ultra-deep desulfurization of benzene

The ultra-deep adsorptive desulfurization (ppb level) of benzene remains a challenging subject with the need to construct efficient adsorbent systems. Herein, a kind of ruthenium-based adsorbent functionalized with bimetallic Ru–Al was rationally designed using Al2O3 as support (denoted as 0.8%Ru-1.2%Al/Al2O3). It was found that the co-anchoring of Ru and Al species endows the Ru-based adsorbent unique adsorption capability, which is able to completely eliminate sulfur compounds in benzene, and exhibiting a much higher breakthrough sulfur capacity than that of the 0.8%Ru/Al2O3. Remarkably, under the industrial experiment conditions, 0.8%Ru-1.2%Al/Al2O3 exhibited excellent long-term stability for more than 1200 h, showing the potential for industrial application. Various characterization techniques, including BET, XRD, SEM, TEM, TPD-MS, TPR and XPS, were used to investigate the correlation between the adsorption performance and the microstructure of the adsorbents. Over 0.8%Ru-1.2%Al/Al2O3, the ultra-thin aluminum additive is beneficial to improve the dispersion of Ru species, which therefore exhibits desirable desulfurization efficiency. Moreover, the enhanced performance is also correlated to the presence of the suitable Ru active centers generated from the selective coverage by Al species. It leads to an optimal exposure of the Ru active centers, which would facilitate the interaction of S–Ru and the improvement of the desulfurization activity.

Sequential Microwave-Assisted Dealumination and Hydrothermal Alkaline Treatments of Y Zeolite for Preparing Hierarchical Mesoporous Zeolite Catalysts

A novel post-synthetic method combining the microwave (MW)-assisted dealumination and hydrothermal (HT) alkaline treatment for obtaining mesoporous Y zeolite catalysts is presented. In the first-step MW-assisted dealumination of the pristine Y zeolite, both the mineral acid (i.e. hydrochloric acid, HCl) and organic carboxylic acids (e.g. oxalic and diethylenetriaminepentaacetic acid) were used (all at 0.16 M), and their effects on the physical and chemical properties of the resulting modified zeolites (after the identical HT alkaline treatment using 0.2 M sodium hydroxide solution) are studied in detail by comprehensive characterisation of the bulk silicon-to-aluminium (SAR) ratio, crystallinity and textural properties. The findings show that, in the developed sequential method, (i) HCl was only effective to achieve the hydrolysis of the zeolite, (ii) carboxylic acids with the function of chelation was very capable of extracting Al species and creating mesopores, and (iii) the mesopores formation is a function of the number of coordination sites in the carboxylic acid. The hierarchical feature of the mesopores in the modified zeolites (using carboxylic acids) was probed by the model reaction of aldol condensation of 1-heptanal with benzaldehyde for the selective formation of jasminaldehyde. The normalised selectivity to jasminaldehyde (with respect to the strong acidity) was proportionally related to the specific mesopores volume of the zeolites, revealing hierarchical porous networks in the relevant modified Y zeolites and indicating the effect of hierarchical mesopores in the zeolites on their catalytic performance.

Bifunctional rice husk-derived SiO2-Cu-Al-Mg nanohybrid catalyst for one-pot conversion of biomass-derived furfural to furfuryl acetate

Developing one-pot reaction methodologies, which typically require multifunctional catalyst systems, is crucial for sustainable production of bio-derived fuels and chemicals. This work reports one-pot hydrogenation-esterification of furfural to furfuryl acetate using a bifunctional metal-based nanohybrid catalyst, composed of rice husk (RH) derived SiO2, Cu, Al, and Mg species (RHSiO2-Cu-Al-Mg). For comparison, the catalytic efficiency of RHSiO2-Cu and RHSiO2-Cu-Al were tested under similar reaction conditions. Various analytical techniques were used to elucidate the physicochemical, textural, and acid-redox properties of the catalysts. It was found that the RHSiO2-Cu-Al-Mg catalyst contains an optimum amount of acid and redox sites, as illustrated by NH3-TPD and H2-TPR studies, respectively. Especially, Mg addition played a vital role in tailoring acidity of the RHSiO2-Cu-Al catalyst to promote in-situ esterification of furfuryl alcohol with acetic acid to yield furfuryl acetate. As a result, the RHSiO2-Cu-Al-Mg catalyst exhibited the best performance in one-pot conversion of furfural to furfuryl acetate, outperforming various noble metal/silica based catalysts. This study offers potential opportunities for the rational design of novel, bifunctional heterogeneous catalysts for efficient production of bio-derived fuels and value added chemicals.

Pd@Al-containing mesoporous silica Yolk–Shell-structured nanospheres as high performance nanoreactors for the selective hydrogenolysis of glucose to 1,2-propylene glycol

In this work, a series of Pd@Al-MSiO2 yolk–shell-structured nanospheres (YSNSs) with different Al contents were synthesized by a facile one-pot method. The EDX elemental analysis and high-magnification TEM image of Pd@Al-MSiO2 YSNSs confirmed that its well-defined yolk-shell structure with a moving Pd core and mesoporous silica shell rich in Al species. Furthermore, Solid state NMR and Py-FTIR results confirmed that Al species grafting mainly formed 4-coordinated Al (AlO4) in the mesoporous silica framework which led to generating abundant Lewis acid sites. The influence of Al species on the physicochemical properties of Pd@Al-MSiO2 YSNSs, as well as their catalytic performance for the hydrogenolysis of glucose to 1,2-propylene glycol (1,2-PG), was investigated. The mesoporous silica shell with abundant Lewis acid sites is a significant contributor to the isomerization of glucose into fructose, while the Pd core plays a role in promoting the hydrogenation of intermediates. The unique hollow space inside the Pd@Al-MSiO2 YSNSs provides a location for the retro-aldol condensation of fructose and consequently avoids direct hydrogenation of fructose. The as-synthesized Pd@Al3-MSiO2 YSNSs shows superior catalytic activity (1,2-PG selectivity of 47.4%, glucose conversion of 95.4%) in the hydrogenolysis of glucose, and far outperforms the Pd/Al3-MSiO2 catalysts. In addition, owing to the influence of the 4-coordinated Al species on the geometry and chemical properties of the mesoporous silica shell, the nanospheres show good stability and reusability over multiple catalytic cycles without significant loss of activity.

Structural evolution of high zirconia aluminosilicate glasses

We report a detailed structural investigation of Ca-Na aluminosilicate glasses containing 0–20 wt% ZrO2 using X-ray absorption spectroscopy, Raman spectroscopy and 27Al and 29Si NMR. The X-ray absorption spectroscopy data reveal that Zr is predominantly present in ZrO6 octahedra but a significant Zr coordination change occurs with increasing ZrO2 content. Though Al and Zr are competing to be surrounded by charge balancing cations, 27Al NMR data do not show the presence of high-coordinated Al species; thus charge-balancing cations are preferentially localized close to AlO4 tetrahedra rather than Zr polyhedra, explaining the increase in Zr coordination number that ultimately leads to limit Zr solubility in glasses. Raman and 29Si NMR data indicates that Zr atoms are linked to the silicate network with a trend for higher degree of network connectivity at high zirconia content. Change in network connectivity and in Zr environment provide insights to understand chemical durability or crystallization in glasses.

Green synthesis of aluminum-hydrochar for the selective isomerization of glucose to fructose

Hydrochar microspheres supported Al catalysts with hierarchically porous structure (Al/HPHMs) for glucose to fructose isomerization were fabricated. Superior catalytic selectivity (93.3%) and fructose yield (32.6%) were achieved in aqueous under 160 °C for 20 min. Hierarchically porous structure was formed after KHCO3 and K2CO3 activation and the roles of KHCO3 and K2CO3 in controlling the Al phase and tailoring morphology of hydrochar supported Al were evaluated. The major active sites were characterized as Al hydroxides including β-Al(OH)3, γ-Al(OH)3, γ-AlO(OH), Al-C-O linkages. Active sites by KHCO3 activation with high contents of Al-C-O and Al(OH)3 have better selectivity. Oxygen-containing functional groups including aluminum‑oxygen groups on the hydrochar microspheres have contributed to the formation of hydrogen bond and π-π interactions between glucose and Al species. Green process synthesized aluminum-hydrochars have potential for their application as a variety of stable, recyclable, and efficient catalysts for lignocellulosic biorefining.

Catalytic reforming of lignite pyrolysis volatiles over sulfated HZSM-5: Significance of the introduced extra-framework Al species

Sulfated HZSM-5 zeolite prepared by dealumination, realumination and sulfation was used as the active mesoporous materials to promote the formation of light aromatics during catalytic reforming of volatiles from Shengli lignite pyrolysis. The results show that HCl-dealumination significantly increased the total pore volume (especially mesopores) and average pore size while reducing acid strength and amount of acid sites. The incorporation of the extra-framework Al species to HZSM-5 combined with SO42− to form superacidic surface sulfate complex exhibited an increase in the yield of light aromatics and a decrease in the yield of coke in comparison with that of original HZSM-5. Among the modified catalysts, SO42−/DHZ5-A (introduced the calcined Al2O3 after HCl-dealumination and modified with (NH4)2SO4) with the acidity enhancement by sulfation obtained the maximum light aromatics yield of 27.3 mg/g and the lowest coke yield of 2.7%. The relationship between the physic-chemical properties of catalysts and the product distribution was proposed to understand the formation of light aromatics.

Control of framework Al distribution in ZSM-5 zeolite via post-synthetic TiCl4 treatment

Evaluating and controlling the distribution of framework Al species in ZSM-5 zeolite, which consists of an orthorhombic MFI framework with 12 tetrahedral sites, are key issues for improving the acid-catalytic properties. The vapor-phase TiCl4 treatment of ZSM-5 at 600 °C led to a drastic change in the framework Al distribution, as confirmed by 27Al magic-angle spinning nuclear magnetic resonance measurements and density functional theory calculations. The maximum of the 27Al NMR peak attributed to framework Al shifted drastically from 55 to 52 ppm following TiCl4 treatment, suggesting that this treatment leads to selective dealumination of the framework Al species corresponding to the peak at 55 ppm. Ti-modified ZSM-5 showed moderate acidity in catalytic reactions such as the ethylene-to-propylene reaction and various cracking reactions. It is suggested that TiCl4 treatment results in the selective release of strong Brønsted acid sites from the MFI framework. Thus, the proposed post-synthetic treatment method provides an effective approach for tuning the catalyti c properties of ZSM-5 zeolite.

The role of synergistic effects between ozone and coagulants (SOC) in the electro-hybrid ozonation-coagulation process

In order to improve the dissolved organic matter removal efficiency, an electro-hybrid ozonation-coagulation (E-HOC) system was developed in this study, in which the electro-coagulation (EC) and ozonation occurred simultaneously in one integrated unit. Higher removal efficiency was observed for the E-HOC process compared with those of EC, ozonation and pre-ozonation-EC process for the treatment of wastewater treatment plant (WWTP) effluent and ibuprofen (IBP). 58.6% dissolved organic carbon (DOC) removal efficiency was achieved in the E-HOC process for the treatment of WWTP effluent at optimal operational condition (current density 15 mA/cm2, initial pH 5 and ozone dosage 1.5 mg O3/mg DOC). Based on the reactive oxygen species (ROS) detection and reactions on the electrodes, the synergistic effects between ozone and coagulants (SOC) were found to be involved in the E-HOC process. According to pseudo-first-order rate constant analyses, the contribution of five possible organic removal pathways was quantified. It was revealed that the peroxone and SOC effects exhibited almost equal contribution to IBP removal at initial pH 5 under different current densities, both of which played the dominant role in the E-HOC process. However, the contribution of the SOC effects decreased significantly when the initial pH increased to 7 and 9. As an important pathway for organic removal in the E-HOC process at initial pH 5, the mechanism of the SOC effects was analysed at initial pH 5. It was revealed the SOC effects can further improve hydroxyl radicals (•OH) generation, and the surface hydroxyl groups of the hydrolysed Al species generated from anode electrolysis were determined to be the active sites to generate ROS in the SOC effects.

Mildly acidic aluminosilicate catalysts for stable performance in ethanol dehydration

Ethanol dehydration is effectively catalyzed by strongly acidic zeolites which, however, exhibit poor time-on-stream stability. For example, HZSM-5 features strong acid sites, catalyzes ethylene oligomerization, and is prone to coking. Alumina and silica-alumina on the other hand have lower acidity, are relatively stable, but reach only low activity. Here, a series of mesoporous aluminosilicate catalysts was prepared by non-hydrolytic sol-gel (NHSG) and are shown to feature an intermediate level of acidity (both in strength and nature), resulting in intermediate catalytic performance. Importantly, the best NHSG-made samples were very stable with time on stream, did not produce any traces of ethylene oligomers, did not show any trace of coke formation, and their texture was unaffected. Characterization (ICP-OES, N2-physisorption, TEM, XPS, IR-pyridine, Raman and solid state NMR spectroscopies) revealed that this behavior must be correlated with the remarkable degree of homogeneity in the NHSG-made aluminosilicate (only tetrahedrally coordinated Al species).

Towards a comparison between the hybrid ozonation-coagulation (HOC) process using Al- and Fe-based coagulants: Performance and mechanism

In this study, the removal performance of a hybrid ozonation-coagulation (HOC) process using AlCl36H2O (Al–HOC) and FeCl36H2O (Fe–HOC) as coagulants for the treatment of wastewater treatment plant (WWTP) effluent and ibuprofen (IBP) was investigated. Compared with the conventional coagulation process and pre-ozonation-coagulation process, much better organic matter removal performance can be achieved for both the Al–HOC and Fe–HOC processes. The Fe–HOC process showed an obviously higher dissolved organic carbon (DOC) removal efficiency than that of the Al–HOC process. Surface hydroxyl groups were determined to be the active sites in generating OH in the HOC process, and the hydrolysed Fe species possessed a higher content of surface hydroxyl groups than the hydrolysed Al species according to fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectra (XPS) analyses. In addition, the hydrolysed Fe species contained a higher portion of tetrahedral sites that were more likely to be stronger Lewis acid sites to react with ozone to generate OH. Furthermore, peroxone reactions in the HOC process were other possible way to enhance the OH generation, and higher H2O2 generation was observed in the Fe–HOC process due to higher O2− generation. Therefore, better removal performance of the Fe–HOC process can be obtained due to the increased OH generation in the Fe–HOC process.

Creation of Al‐Enriched Mesoporous ZSM‐5 Nanoboxes with High Catalytic Activity: Converting Tetrahedral Extra‐Framework Al into Framework Sites by Post Treatment

AbstractZSM‐5 zeolite nanoboxes with accessible meso‐micro‐pore architecture and strong acid sites are important in relevant heterogeneous catalysis suffering from mass transfer limitations and weak acidities. Rational design of parent zeolites with concentrated and non‐protective coordination of Al species can facilitate post‐synthetic treatment to produce mesoporous ZSM‐5 nanoboxes. In this work, a simple and effective method was developed to convert parent MFI zeolites with tetrahedral extra‐framework Al into Al‐enriched mesoporous ZSM‐5 nanoboxes with low silicon‐to‐aluminium ratios of ≈16. The parent MFI zeolite was prepared by rapid ageing of the zeolite sol gel synthesis mixture. The accessibility to the meso‐micro‐porous intra‐crystalline network was probed systematically by comparative pulsed field gradient nuclear magnetic resonance diffusion measurements, which, together with the strong acidity of nanoboxes, provided superb catalytic activity and longevity in hydrocarbon cracking for propylene production.

Creation of Al-Enriched Mesoporous ZSM-5 Nanoboxes with High Catalytic Activity: Converting Tetrahedral Extra-Framework Al into Framework Sites by Post Treatment.

ZSM‐5 zeolite nanoboxes with accessible meso‐micro‐pore architecture and strong acid sites are important in relevant heterogeneous catalysis suffering from mass transfer limitations and weak acidities. Rational design of parent zeolites with concentrated and non‐protective coordination of Al species can facilitate post‐synthetic treatment to produce mesoporous ZSM‐5 nanoboxes. In this work, a simple and effective method was developed to convert parent MFI zeolites with tetrahedral extra‐framework Al into Al‐enriched mesoporous ZSM‐5 nanoboxes with low silicon‐to‐aluminium ratios of ≈16. The parent MFI zeolite was prepared by rapid ageing of the zeolite sol gel synthesis mixture. The accessibility to the meso‐micro‐porous intra‐crystalline network was probed systematically by comparative pulsed field gradient nuclear magnetic resonance diffusion measurements, which, together with the strong acidity of nanoboxes, provided superb catalytic activity and longevity in hydrocarbon cracking for propylene production.

Mesoscale depolymerization of natural rectorite mineral via a quasi-solid-phase approach for zeolite synthesis

Synthesis of zeolites from natural aluminosilicate minerals is a green and sustainable technology. One major challenge in the synthesis is how to enhance the reactivity of the natural minerals. Herein we developed a facile quasi-solid-phase method to efficiently depolymerize natural rectorite into its corresponding mesoscale building blocks, i.e., TO4 (T = Si or Al) monomers or oligomeric species. Natural rectorite can be completely and efficiently depolymerized at 170 °C within 60 min, which is substantially lower than temperatures (>900 °C) used in industrial depolymerization methods. The transformation of Si and Al species in the QSP depolymerization mainly undergoes three stages: (1) the layer of Na6AlVI4AlIV2Si6O24·nH2O is dissociated and converted into Na6AlVI2AlIV4Si6O24; (2) Na6AlVI2AlIV4Si6O24 is further depolymerized into Na4AlIV4Si6O20 and monomer NaAlIVO2; (3) Na4AlIV4Si6O20 is finally decomposed into mesoscale monomers (Na4SiO4 and NaAlIVO2), dimers (Na6Si2O7), and chains (Na2SiO3). Moreover, the depolymerized rectorites exhibits high reactivity for synthesizing highly crystalline ZSM-5 zeolite.

Effect of in-situ formed Al hydrates through long-term aging on enhanced particle destabilization by PACl coagulation

Aging of polyaluminum chloride (PACl) coagulants could significantly influence hydrolyzed Al speciation ruling coagulation performance. The goal of this study was to investigate Al species transformation through long-term aging and its impact on coagulation performance. Two kinds of commercial coagulants (PACl-1 and PACl-2) were stored for in-situ aging tests in six months to evaluate Al species variation with time and the performance of coagulation with natural turbid waters. The results showed that CaSO4 precipitation easily occur in a commercial PACl coagulant with time as it contains SO42− and Ca2+. It also activates the precipitation of gibbsite Al(OH)3 in PACl with aging. Through 180 days aging, both monomeric Al (Ala) and polymeric Al (Alb) substantially transform into colloidal Al (Alc) and precipitated for both PACl coagulants. At low turbidity (10 NTU), PACl-1 has a superior turbidity reduction rate than PACl-2, while PACl-2 performs a little better turbidity reduction at high turbidity (1000 NTU) regardless of aging time. With aging time, an obvious decrease in turbidity reduction for PACl-1 coagulation is observed at low turbidity of 10 NTU, while the improvement in turbidity reduction for PACl-2 coagulation by enhanced sweep flocculation can be achieved as Alb mostly transform into Alc after 150 days aging. It is concluded that dominant in-situ formed Alc after a long time hydrolysis can improve PACl coagulation efficiency in turbidity reduction by enhanced sweep flocculation, especially for low turbidity water, but the increase in preformed Alc in PACl would worsen particle destabilization after aging.