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A rapid and efficient synthesis strategy of MgAl-LDH was proposed. MgAl-LDH with high specific surface area was synthesized in situ by using η-Al2O3 as carrier, and the synthesis time was greatly shortened by both increasing temperature and introducing ethanol as co-solvent. Besides, the growth process of MgAl-LDH on the surface of η-Al2O3 is also revealed. Under optimized conditions, the specific surface area of the MgAl-LDH is as high as 172.4 m2/g, the crystalline size is as small as 12.82 nm, and the basicity can reach 1.795 mmol/g. The urea wastewater was degraded from 8000 mg/L to 6.85 mg/L over the catalyst synthesized by the rapid method, and the catalyst still maintains high activity after four uses. Also, it was found that there is a good linear relationship between the urea removal rate and the basicity of MgAl-LDH. more...

MnO2 was screened from various metal oxides and different crystal structures of MnO2 were prepared, which were used to hydrolyze urea process wastewater for energy conservation and environmental protection. The characterizations of XRD, SEM, Raman, FT-IR, XPS and H2-TPR were employed and the hydrolysis experiments were carried out, demonstrating that oxygen vacancy on the surface of MnO2 might be the catalytic activity source on urea hydrolysis. By optimizing reaction influencing factors, the residual urea concentration reduced to 1.61 mg/L over α-MnO2, far below the effluent standard. Meanwhile, the temperature of heterogeneous hydrolysis over α-MnO2 dropped drastically compared with that of thermal hydrolysis. Further, the kinetic parameters of hydrolysis were obtained over α-MnO2. And α-MnO2 also showed excellent recycling ability on the reused test. more...

High value-added utilization of plastic waste has historically been a problem, which has driven researchers to make long-term and unremitting efforts to tackle it. High-performance carbon based solid acid (CSA) was prepared from polyvinyl chloride (PVC) and polyethylene (PE) in different proportions. The small amount of chlorine is still residual on the edge of graphitic carbon sheets after co-carbonization and sulfonation. Strong electronegative –Cl group and the high-density phenolic –OH group, double-adsorption group, are covalently bonded to the edges of the graphitic carbon sheets, contributing to the decrystallization of cellulose to a large extent. Meanwhile, PVC and PE-derived CSAs have significantly higher –SO3H group density than PVC-derived CSA and cellulose-derived CSA. These are obviously beneficial to the improvement of hydrolysis activity, which can be attributed to structural optimization caused by co-carbonization PVC and PE. The CSA with a mixture of 80% proportions has great catalytic activity and repeatability. more...

Magnesium aluminum layered double hydroxide (MgAl–LDH) was first successfully deposited in situ on η-Al2O3 applied to catalyze urea hydrolysis. Characterization by AAS, XRD, SEM, EDS, DSC, FT-IR, N2-BET, determination of base strength and basicity and experiments on hydrolysis activities of in situ MgAl–LDH catalysts show that the crystallinity and coverage degree of MgAl–LDH on η-Al2O3 gradually increase with increasing initial c(Mg2+). When initial c(Mg2+) = 2 mol L−1, η-Al2O3 is completely covered and the smallest particle size, the highest crystallinity, basicity and urea degradation rate of in situ MgAl–LDH are obtained. The basicity is mainly from Mg–OH at the edges of MgAl–LDH on η-Al2O3. The highest basicity corresponds to the highest urea degradation rate, Mg–OH is the active sites for catalytic hydrolysis of urea. The specific surface area, basicity and catalytic activity of MgAl–LDH by in situ synthesis are evidently higher than MgO and MgAl–LDH purchased. The urea concentration is 8.162 mg L−1 at 165 °C after 120 min with in situ MgAl–LDH (c(Mg2+) = 2 mol L−1) as catalyst, which is below the effluent standard. In situ MgAl–LDH also shows excellent recycling ability and the slight loss of activity should be due to the reduction of basicity, which is caused by hydrothermal conditions. In addition, a possible catalytic mechanism of urea hydrolysis over MgAl–LDH is proposed. more...

Carbon based solid acids (CSAs) were prepared from cellulose and lignin at different carbonization temperatures and applied to hydrolysis of cellulose, which is of great significance for the multiple utilization of biomass. The structure and performance of cellulose based solid acids (CCSAs) and lignin based solid acids (LCSAs) were investigated by TG-DTG, XRD, FT-IR, XPS, elemental analysis, titration methods, etc. And immersion enthalpy was introduced into estimating the hydrophilicity of CSAs. The results show that the optimum carbonization temperature varies for raw material, and the optimum carbonization temperatures of cellulose and lignin are 683 and 653 K respectively. The adsorption capacities of CCSAs and LCSAs may not only be related to phenolic OH density, but may also relate to alkyl side chains and aromatic frameworks. Compared with LCSAs, the CCSAs possess higher immersion enthalpy, indicating that the CCSAs are more easily accessible to substrate, which contributes to hydrolysis. The hydrolysis activities of CCSAs are always higher than those of LCSAs, which may be due to a higher –SO3H groups densities and better accessibility between substrate and acid sites for CCSAs. These are determined by a big difference in the chemical composition between cellulose and lignin. more...

A novel metal-free solid acid was prepared by co‑carbonation followed sulfonation, using cellulose and sodium thiosulfate as raw materials. The effects of sulfur-doping on the structure and catalytic activity of the solid acid were discussed. The results reveal that S content of the solid acid was up to 23.53 wt%, in which S was present in the form of sulfoxide, sulfone, thiophene and disulfide groups in addition to sulfonic acid group. The solid acid exhibited high adsorption capacity and catalytic activity in cellulose hydrolysis compared with carbon-based solid acid, which is initially attributed to the appearance of sulfoxide and thiophene. Sulfoxide and thiophene can enhance the adsorption capacity of the solid acid through hydrogen bonding and CH-π interaction respectively, leading to improvement in hydrolytic activity of the solid acid. more...

A series of carbon-based solid acids (CSAs) were respectively prepared by the different relative proportions of cellulose and lignin to simulate biomass, and employed to hydrolyze cellulose. The influence of relative proportions of cellulose and lignin on mixture-derived CSA (MCSA) has been investigated in detail. Differences in the structure and performance of MCSAs were found to be obvious. The microcrystalline structure parameters, adsorption capability and hydrolysis activity of MCSA present regular variation trend with the increase of cellulose proportions, which can be attributed to the interaction of cellulose and lignin during co-carbonization. When cellulose proportion is 50%, the co-carbonization is at a turning point, the carbon skeleton of MCSA is more flexible and disordered with larger interlamellar spacing and more C O C bond. Meanwhile, MCSA exhibits remarkable adsorption capability, and the hydrolysis activity is comparable to that of cellulose-derived CSA. more...

High-performance carbon-based solid acid was prepared by a simple method. The effects of carbonization temperature and mixing ratio on the structure and performance of carbon catalysts were explored. The participation of borax increases both –COOH group and –SO3H group densities. In addition, graphitization and specific surface area of the catalyst increase by this co-carbonization method. Higher –COOH group density and aromaticity facilitate the adsorption between catalyst and substrate molecule through hydrogen bonding and CH-π interaction respectively. These improvements of structural significantly increase the hydrolysis activity of the catalyst. more...

In order to solve the problem that loading chlorine could reduce the density of -SO3H group and inhibit the increase of catalytic activity, three strategies were adopted to realize the simultaneous chlorination and oxidation modification of carbon-based solid acid, using cheap and easily available NaClO and highly reactive coal as raw materials. The results show that the involvement of NaClO changes the structure of coal-based solid acid from three aspects: loading of chlorine, increase of −COOH group and improvement of aromaticity. It is worth mentioning that −COOH group plays a dual role in both adsorption and hydrolysis, which has a compensation effect on -SO3H group and -Cl group. The structural improvement prominently enhances the hydrolysis of cellulose. Moreover, −COOH group and -Cl group with induced effect can significantly improve the stability of solid acid. more...

Pyrolysis techniques can provide a way to convert polyvinyl chloride (PVC) waste into high value liquids and gases. The inexpensive pyrolysis residue was used to successfully prepare a carbon-based solid acid (CSA) bearing –Cl functional group by a simple process, which has been shown to be highly effective for hydrolyzing microcrystalline cellulose into reducing sugars. The structure, acidic functional group density and catalytic activity of PVC-derived CSA (PCSA) were investigated. The results showed that the carbonization time has an important influence on the structure and properties of the PCSA, especially in a lower temperature range. There was a compensation effect between the carbonization temperature and time on the structure and the activity of PCSA. Phenolic-OH and –Cl groups acted as double cellulose-binding sites and together improved the adsorbability of PCSA, which is much higher than that of traditional CSA and other CSAs bearing –Cl groups. The high hydrolytic activity was determined by the adequate density of the –SO3H group, the excellent adsorption property, and the entire structure of the PCSA. more...

A carbon-based solid acid (CSA) was prepared from phenolic residue which is the solid waste generated from the refining of crude phenol. Influence of various reaction conditions on hydrolysis of cellulose over phenolic residue-derived solid acid (PRCSA) is discussed. The results indicate that both cellulose hydrolysis and the effectiveness of PRCSA need a suitable temperature range. The glucose can be adsorbed on the surface of PRCSA due to the hydroxyl-rich structure of PRCSA. The behavior of generated glucose in competitive adsorption with unreacted cellulose on PRCSA suppresses the continuing hydrolysis of cellulose to some extent. For PRCSA, the number of effective active sites increases with the decrease of catalyst particle size. In heterogeneous hydrolysis of cellulose assisted by inorganic salts, the promotion of KCl and NaCl is remarkable, which is attributed to the decrystallization of chloride ions on cellulose and the ion exchange between cations and H + in –SO 3 H bonded to PRCSA. more...

Carbon-based solid acid (CSA) was successfully prepared using phenolic residue as starting material. The characterization results indicate that such solid acid catalyst mainly consists of four building blocks: the condensed aromatic carbon sheets, the active groups (including SO3H, COOH and phenolic OH), the side chains (including CH3 and OCH3) and the bridge linkages (including O , CH2 , CH2 CH2 , and OCH2 ) acting as the intermediates between aromatic clusters. Most of these building blocks, except for the SO3H, could be derived from the corresponding part of the phenolic residue. Aliphatic side chains have been demonstrated to greatly improve the sulfonation activity of carbon precursor and promote the catalytic performance in cellulose hydrolysis, and the carbon-based catalyst sulfonated for just 1 h could exhibit almost similar catalytic activity compared with the catalyst sulfonated for a longer time. However, their hydrophobicity and steric hindrance reduced the utilization efficiency of the sulfonic acid groups to a certain extent. more...

A carbon-based solid acid was successfully synthesized by sulfonating a carbon precursor from pyrolysis of phenol residue, which is a solid waste from coking industry and contains higher phenols. The unit structures of the phenolic residual-based solid acid are fused aromatic rings bearing CH3 side chains besides phenolic-OH, COOH and SO3H groups. The direct pyrolysis and carbonization process of phenol residue abounding in phenolic hydroxyl groups avoids the loss of sulfonic acid groups instead of low temperature carbonization in concentrated sulfuric acid. Reaction kinetics of sucrose heterogeneous hydrolysis over the solid acid was studied to assess its catalytic activity and stability. The results indicate that the carbonization temperature for the preparation of carbon precursor significantly affects the catalytic performance of the solid acid because of the difference in the compact degree of carbon skeleton. The activation energy calculated is 74.67 kJ mol−1, which reveals good catalytic activity. And the catalyst is fairly stable after repeatedly being used five times. It can substitute enzymes and sulfuric acid in sucrose hydrolysis. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd. more...

In order to find an effective method for treating urea wastewater, the experiments on the hydrolysis of urea in wastewater were conducted in a fixed bed reactor with different aluminas (α-Al2O3, γ-Al2O3, and η-Al2O3) as catalysts respectively in contrast with inert ceramic particle. The results indicate that the three alumina catalysts show obvious catalytic activity for urea hydrolysis at 125 °C. The order of activity is η-Al2O3 > γ-Al2O3 > α-Al2O3, and the activity difference increases with increasing temperature. According to the characterization results, surface acidity has little impact on the activity of catalyst. However, it was found that surface basicity of alumina catalyst plays an important role in catalytic hydrolysis of urea, and the activity of catalyst may be also influenced by the basic strength. With η-Al2O3 as catalyst, the urea concentration in wastewater is reduced to 4.96 mg/L at a temperature of 165 °C. Moreover, the η-Al2O3 shows a good stability for urea hydrolysis. The hydrolysis of urea over η-Al2O3 catalyst can evidently reduce the reaction temperature and is promising to replace industrial thermal hydrolysis process. more...