Concentration Of Acid Sites Research Articles

Low-temperature one-step synthesis of surfactant-free ZnO nanoparticles for efficient glycolysis of PET

Among PET chemical recycling technologies, glycolysis has shown the greatest potential for achieving commercial viability on large scales. The catalyst development is always one of the challenges in PET glycolysis. Herein, surfactant-free ZnO nanoparticles (SF-ZnO) were synthesized through a one-step process in an aqueous medium at low temperatures and ambient pressure. Meanwhile, a microchannel reactor with intensified micro-mixing and mass transfer was used to finely control the synthesis of SF-ZnO with uniform size distribution and consistent production reproducibility. Compared to the modified ZnO nanoparticles (M−ZnO) treated with the surfactant KH570, SF-ZnO exhibited enhanced catalytic activity and reusability in PET glycolysis, which can be attributed to its higher concentration of acid sites and superior thermal stability. Response surface methodology (RSM) was employed to investigate the impact of four key factors (temperature, time, catalyst: PET mass ratio, EG: PET mass ratio) and their interactions on bis(2-hydroxyethyl) terephthalate (BHET) yield in PET glycolysis. Under optimal conditions (196 °C, 40 min, SF-ZnO: PET = 0.76 wt%, EG: PET = 4), PET conversion and BHET yield reached 100 % and 97.3 %, respectively. Aspen simulation and preliminary scale-up experiments confirmed the commercialization potential of PET glycolysis on SF-ZnO. Meanwhile, the environmental energy impact metric and life cycle assessment (LCA) showed that the SF-ZnO catalytic system provided an economically feasible and environmentally friendly solution to PET glycolysis.

Modulating the Microstructure and Surface Acidity of MnO2 by Doping-Induced Phase Transition for Simultaneous Removal of Toluene and NOx at Low Temperature.

It is a great challenge to remove VOCs and NOx simultaneously from flue gas in nonelectric industries. This study focuses on the construction of Fe-MnO2 catalysts that perform well in the simultaneous removal of toluene and NOx at low temperatures. Utilizing the Fe-induced phase transition of MnO2, Fe-MnO2-F&R catalysts with a composite morphology of nanoflowers and nanorods were successfully prepared that provided an abundant microporous structure to facilitate the diffusion of molecules of different sizes. Through in-depth investigation of the active sites and reaction mechanism, we discovered that Fe-induced phase transition could modulate the surface acidity of Fe-MnO2-F&R. The higher concentration of surface Mn4+ provided numerous Brønsted acid sites, which effectively promoted the activation of toluene to reactive intermediates, such as benzyl alcohol/benzoate/maleic acid. Simultaneously, Fe provided a large number of Lewis acid sites that anchor and activate NH3 species, thereby inhibiting NH3 nonselective oxidation. Furthermore, additional Brønsted acid sites were generated during the simultaneous reaction process, enhancing toluene activation. Consequently, the simultaneous removal of toluene and NOx was achieved through regulation of the physical structure and the concentration of acidic sites. The present work provides new insights into the rational design of bifunctional catalysts for the synergistic control of VOCs and NOx emissions.

NH3-probe X-ray photoelectron spectroscopy method to characterize solid acidity of clay minerals

Accurate determination of solid acidity is essential for evaluating the catalytic activity of clay minerals. However, the conventional Fourier-transform infrared (FTIR) method using NH3 as the probe encounters challenges in measuring the solid acidity owing to the presence of water on the surface or within interlayer spaces of clay minerals as well as the influence of environmental water during the detection process. To mitigate water interference, a NH3-probe X-ray photoelectron spectroscopy (XPS) approach was adopted as an alternative to the FTIR method for the identification and semi-quantification of solid acidity of clay minerals. Following NH3 adsorption, the types of solid acid sites in clay minerals were identified through the chemical shift in N1s XPS spectra. The ratio of Brønsted and Lewis acid sites in a given sample and the relative concentration of acid sites across different samples were determined by examining the specific N1s peak area ratio. According to the XPS data, the ratios of Brønsted and Lewis acid sites in Ca-montmorillonite (SAz-2) and Na-montmorillonite (SWy-2) were nearly 1:1, whereas that for the illite–smectite mixed-layer mineral (ISCz-1) was 4. The acid site contents in SAz-2 were more than twice those of SWy-2. This work highlights the promising application prospects of the NH3-probe XPS method in solid acidity investigations of clay minerals.

Dehydration of lactic acid to prepare acrylic acid over Hβ zeolite modified by acid treatment and Rb ion-exchange

The catalytic dehydration of bio-derived lactic acid into acrylic acid is one of the research hotspots in the field of green chemical industry, but the selectivity of acrylic acid and the stability of catalyst still face great challenges. In this work, a modified Hβ zeolite catalyst was prepared by sequential nitric acid treatment and Rb ion-exchange for the gas phase dehydration of lactic acid to prepare acrylic acid. The nitric acid treatment increased the content of Lewis acid sites together with the decrease of the content of Bronsted acid sites, which enhanced the dehydration and hindered the decarboxylation/decarbonylation of lactic acid. Consequently, the selectivity of acrylic acid was improved. The Rb ion-exchange not only significantly decreased the density of acidic sites but also regulated the density of basic sites of the catalyst. The optimal 0.1NA-6.8Rb/Hβ catalyst treated by 0.1 mol/L of nitric acid and 6.8 wt% of Rb ion-exchange contributed to a 99.28 % conversion of lactic acid and 76.72 % yield of acrylic acid. The catalyst showed a better stability and was easy to regenerate, maintaining 87.35 % conversion of lactic acid and 62.49 % yield of acrylic acid, respectively, after two cycles of consecutive 48 h reaction.

Promote the efficient co-combustion of toluene & CO in Pt/CeO2 catalyst: Orientally adjusting the oxidized SMSI to optimize acid site and oxygen vacancy

By effectively controlling the strong metal-support interaction (SMSI), the formation of acid sites and oxygen vacancies (Ov) on the Pt/CeO2 catalyst was optimized. The efficient co-combustion of toluene and CO on Pt/CeO2-450 was achieved. In the dual-pollutant system, when the conversion rate was 90 %, the corresponding conversion temperatures of toluene and CO were 165 °C and 173 °C, respectively. With the increase of SMSI, the catalytic activity of Pt/CeO2 showed a trend of first increase and then decrease. This was proportional to the content of weak acid sites, medium acid sites, and Ov generated on their surfaces. Compared with the combustion of a single pollutant, the result displays that toluene and CO had significant competitive adsorption on Pt/CeO2. The inhibition of toluene on CO also showed the same trend as the catalytic activity with the increase of SMSI. Under the double inhibition, Pt/CeO2 exhibited preferential selectivity for toluene combustion. However, the in situ DRIFTS results showed that this competitive adsorption phenomenon did not interfere with the combustion reaction path. The co-combustion of toluene and CO follows independent reaction paths. This work provides valuable insights and ideas for realizing the development of efficient and environmentally friendly catalysts through SMSI regulation.

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

Furfural Acetalization with Ethanol over Hierarchical vs. Conventional Beta Zeolites

AbstractA set of hierarchical Beta zeolites was synthesized using concentrated reaction mixtures and compared to conventional materials with a similar composition. The obtained zeolite catalysts were investigated in acetalization of furfural with ethanol at room temperature yielding a commercially valuable fuel additive (furfural diethyl acetal). The highest yield of the desired product (91 %) was achieved over a zeolite catalyst possessing developed mesoporosity (Vmeso 0.75 cm3/g) and a high external surface area (280 m2/g). The concentration of accessible acid sites was found to be responsible for high catalytic performance of the tested zeolitic catalysts.

Dechlorination of a real plastic waste pyrolysis oil by adsorption with zeolites

The adsorptive dechlorination of a pyrolysis oil coming from real plastic waste was investigated using different Na-zeolites (4A, 13X, and Y) as adsorbents. The dechlorination experiments were performed in a fixed bed trap under inert atmosphere operating at moderate temperatures (< 180 °C). The dechlorination efficiency of the adsorbents was significantly improved by performing a dehydration pre-treatment due to the removal of water molecules physisorbed on the zeolite surface. Among the zeolitic materials tested, 13X zeolite showed the best dechlorination efficiency, which was related to its high content of Lewis acid sites (attributed to the presence of Na+ cations ionically interacting with the zeolite framework), acting as chemisorption sites, as well as the high accessibility of the FAU-zeolitic topology to the Cl-containing compounds. For that sample, a detailed study of the adsorption temperature (from 30 to 180 °C) and time on stream (1–6 h) was further carried out. The maximum chlorine removal efficiency was achieved, reducing the chlorine content of the pyrolysis oil from 421 to 45 ppm, at temperatures of about 150 – 180 °C. Interestingly, under these conditions, thermal or catalytic cracking effects of the zeolite on the feedstock were not observed. However, the study of the time on stream showed that, after 3 h, the chlorine removal efficiency of the zeolite started to decrease. Thus, different regeneration treatments were evaluated proving that, after a combustion at 600 °C, the zeolite recovered its initial dechlorination efficiency. This research reveals the potential of the adsorptive dechlorination process with Na-zeolites to reduce the chlorine content in plastic pyrolysis oils under mild operating conditions.

Cu/ZnO/Al2O3 sorbent promoted by Zr for the ultra-deep removal of thiophene in simulated coke oven gas

The ultra-deep removal of thiophene from coke oven gas (COG) is critical for the conversion of COG to methane. Currently, Cu/ZnO/Al2O3 is considered as a promising sorbent for thiophene removal; however, its desulfurization performance is currently unable to meet the requirements for industrial applications. Here, a zirconium modification strategy is proposed to overcome this problem, allowing zirconium loaded copper-based sorbents (Cu/ZnO/Al2O3/ZrO2) with significantly improved thiophene removal performance and high activity to be obtained. Characterization results showed that zirconium improved both the dispersion of copper and the concentration of Lewis acid sites on the sorbent surface. A ZrO2 concentration of 2 % resulted in stronger Cu-Zn interaction, and the dispersion of Cu on the surface of the sorbent reached its maximum value (49.20 %). Additionally, the Lewis acid strength was also maximized, which greatly improved the desulfurization activity and resulted in a breakthrough adsorption capacity of thiophene (Qb-thiophene) of 36.24 mg/g, which was about 17 % higher than that of the unmodified Cu/ZnO/Al2O3 sorbent. These results demonstrate that the sulfur capacity of the sorbent can be increased by increasing the number of acidic sites on its surface, paving the way for ultra-deep thiophene removal in industrial applications.

Synthesizing a transesterification catalyst via a condensation reaction and assessment of the mechanism using density functional theory

AbstractBACKGROUNDA solid acid (SPEI–EN–OHCMs) having dendritic –NH2 groups was prepared via oxidation of hydrothermal carbon microspheres (OHCMs) followed by a condensation reaction with the –NH2 groups of polyethyleneimine and sulfonation. The mechanism by which –COOH groups on the surfaces of OHCMs reacted with these –NH2 groups was assessed using density functional theory (DFT).RESULTActivation using a combination of 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride (EDC) and N‐hydroxysuccinimide (NHS) was found to promote the formation of amide bonds such that –NH2 groups were bonded to the microsphere surfaces. This effect provided more bonding sites for –SO3H groups. The DFT results indicated that the energy barrier on the potential energy surface in the presence of EDC and NHS was lowered by 18.1 kcal mol−1. X‐ray photoelectron spectroscopy analyses also confirmed the introduction of –NH2 groups followed by –SO3H groups onto the surfaces of the OHCMs. The concentration of surface acid sites on SPEI–EN–OHCMs was found to be as high as 11.8 mmol g−1. Thermogravimetric data and elemental analysis results showed that the –SO3H groups on the SPEI–EN–OHCM surfaces were thermally stable below 180 °C.CONCLUSIONThe SPEI–EN–OHCMs catalyst was used to promote the transesterification reaction of waste frying oil with methanol. A trial with a methanol‐to‐oil molar ratio of 10:1 at 110 °C for 4 h gave a fatty acid methyl ester (FAME) yield of 92.3%. After four reuses, an SPEI–EN–OHCMs specimen provided a FAME yield of 54.3%. © 2024 Society of Chemical Industry (SCI).

Hydrodeoxygenation of mixtures of biomass-derived model compound oxygenates over Pt/HY catalysts

In this study, a systematic analysis of the effect of three biomass pyrolysis oxygenates, viz., acetic acid, cyclopentanone and furfural, on the hydrodeoxygenation (HDO) of guaiacol is performed. Bifunctional Pt/HY catalysts with different Si/Al ratios were screened for the HDO of guaiacol. Guaiacol conversion and the cyclohexane yield increased with the concentration of acid sites in the zeolites. The presence of acetic acid and cyclopentanone did not affect the guaiacol conversion and the product selectivity, while guaiacol conversion decreased significantly in the presence of furfural. The effects of temperature, reaction time, and the guaiacol-furfural molar ratio on the HDO of guaiacol were studied. The time evolution of products showed that the furan ring opening influences the conversion of guaiacol.Quantum chemicaldensity functional theorycalculations using individual and binary model compounds revealed the decrease in adsorption energy of guaiacol over Pt (111) in the presence of furfural.

Tailoring the Brønsted acidity of Ti-OH species by regulating Pt-TiO2 interaction.

Bifunctional catalysts comprising metal and acid sites are commonly used for many reactions. Interfacial acid sites impact intermediate reactions more than other sites. However, controlling the type and amounts of interfacial acid sites by regulating metal-support interaction (MSI) via traditional methods is difficult. Thus, the influence of MSI on interfacial acid sites remains unclear. We prepared Pt-mTiO2/α-Al2O3 (m represents the cycle number of TiO2) catalysts via atomic layer deposition (ALD). New Brønsted acid sites were generated via Pt-TiO2 interaction, and the acidity was precisely regulated by regulating Pt-TiO2 interaction by changing the TiO2 nanolayer thickness. We chose levulinic acid (LA) hydrogenation as a model reaction. The catalytic activity varied with the TiO2 nanolayer thickness and was linearly correlated with the Ti-OH species (Brønsted acid) content. Pt-40TiO2/α-Al2O3, with the highest acid site content of 0.486 mmol/g, exhibited the best catalytic activity. Hydrogen spillover and water dissociation at the Pt-TiO2 interface promoted Ti-OH species generation.

Impact of Low-Temperature Water Exposure and Removal on Zeolite HY.

Aqueous-phase postsynthetic modifications of the industrially important Y-type zeolite are commonly used to change overall acid site concentrations, introduce stabilizing rare-earth cations, impart bifunctional character through metal cation exchange, and tailor the distribution of Brønsted and Lewis acid sites. Zeolite Y is known to undergo framework degradation in the presence of both vapor- and liquid-phase water at temperatures exceeding 100 °C, and rare-earth exchanged and stabilized HY catalysts are commonly used for fluidized catalytic cracking due to their increased hydrothermal resilience. Here, using detailed spectroscopy, crystallography, and flow-reactor experiments, we reveal unexpected decreases in Brønsted acid site (BAS) density for zeolite HY following exposure even to room-temperature liquid water. These data indicate that aqueous-phase ion-exchange procedures commonly used to modify zeolite Y are impacted by the liquid water and its removal, even when fractional heating rates and inert conditions much less severe than standard practice are used for catalyst dehydration. X-ray diffraction, thermogravimetric, and spectroscopic analyses reveal that the majority of framework degradation occurs during the removal of a strongly bound water fraction in HY, which does not form when NH4Y is immersed in liquid water and which leads to reduced acidity in HY even when dehydration conditions much milder than those typically practiced are employed. Na+-exchanged HY prepared via room-temperature aqueous dissolution demonstrates that Brønsted acid sites are lost in excess of the theoretical maximum that is possible from sodium titration. The structural impact of low-temperature aqueous-phase ion-exchange methods complicates the interpretation of subsequent data and likely explains the wide variation in reported acid site concentrations and catalytic activity of HY zeolites with high-Al content.

Synthesis of hierarchically radiated SAPO-11/Silica composites to boost n-alkane hydroisomerization

Hierarchically radiated SAPO-11 molecular sieves (RS-11-x, x was the initial SiO2/Al2O3 molar ratio) were prepared by employing different amounts of un-calcined radiated mesoporous SiO2 nanoparticles (RMSNs) as silicon source and template, and the corresponding Pt-based catalysts were applied for n-decane hydroisomerization. During the synthesis of RS-11-x, RMSNs were hydrolyzed into active Si species slowly due to the supporting of CTAB in their channels, and these active Si species interacted with Al and P species on the RMSNs to generate SAPO-11 crystal nuclei. Ultimately, hierarchical SAPO-11 molecular sieves with radiated morphologies were dispersed on the RMSNs. Among RS-11-x, RS-11-0.4 possessed the greatest medium and strong Brønsted acid sites (MSBAS) content (14.9 μmol/g) as well as superior external surface area (247 m2 g−1) and mesopore volume (0.433 cm3 g−1). Furthermore, compared with the SAPO-11 synthesized by tetraethyl orthosilicate (TEOS) and the mixture of CTAB and TEOS as silicon precursors, respectively, RS-11-0.4 possessed a larger external surface area, a higher mesopore volume and the optimal MSBAS content. Consequently, the Pt/RS-11-0.4 catalyst showed a higher selectivity of branched C10 isomers (93.5%), a better selectivity of multi-branched C10 isomers (33.8%), and a lower cracking selectivity (6.3%) than the counterpart catalysts. This work offers a new strategy for preparing hierarchical molecular sieves with superior catalytic performances.

Synthesis of Porous Amorphous SiO2−Al2O3 Solid Acid Catalyst for Efficiently Catalyzing GVL Decarboxylation to Butene

AbstractIn this study, porous amorphous SiO2−Al2O3 (ASA(Si/Al=x)) with different Si/Al ratios was synthesized by gel‐gel method, and used to catalyze green renewable energy source γ‐valerolactone (GVL) to butene. Research indicated that all prepared catalysts had large amounts of disordered mesoporous with the pore size in range of 2–13 nm. For the optimal ASA(Si/Al=20) catalyst, its specific surface area is 430.20 m2 g−l and pore size is about 8.13 nm. Due to the presence of suitable Al species, ASA(Si/Al=20) has the largest Brønsted/Lewis ratio and 0.5554 mmol g−1 weak acid site content. Under the optimized reaction conditions, 90 % butene yield can be obtained in 180 min at 300 °C. In addition, the regeneration performance of the ASA(Si/Al=20) catalyst is also satisfactory, and the yield of butene can be above 60 % after 5th cycles. After activation, the spent catalyst can be regenerated, and about 78 % butene yield can be also obtained.

Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks.

Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone.

Tuning the acidity of SAPO-34 zeolite through niobium incorporation for enhanced catalytic performance during MTO reaction

SAPO-34 zeolite is commonly used for light olefin production, an important petrochemical, through the methanol-to-olefin (MTO) conversion process. To modify the physicochemical characteristics of the SAPO-34 zeolite, a series of Nb-incorporated SAPO-34 catalysts were synthesized to alter the crystal size and acidity of the catalysts to enhance its MTO catalytic properties. The Nb incorporation reduced crystal size from 4.6 μm to 1.4 μm, with enhanced acidity for the Nb0.005SP catalyst. The catalytic results revealed that the Nb0.005SP catalyst showed remarkably superior MTO conversions, ∼2.5 time as compared with conventional SP catalyst, due to its reduced crystal size, higher surface area and higher acid sites concentration owing to its shorter diffusion pathlength, greater number of exposed active sites and ability to maintain MTO reaction for longer time, respectively. Moreover, the Nb0.005SP catalyst also exhibited a lower hydrogen transfer index-HTI index with a slight slope, leading to slower coking, enhanced light olefine selectivity and a longer lifetime compared to other counterparts.

Sustainable catalysts for esterification: Sulfonated carbon spheres from biomass waste using hydrothermal carbonization

Sulfonated catalysts derived from carbon spheres obtained from açai seeds (Euterpe oleracea) were synthesized using a hydrothermal carbonization method, followed by subsequent direct sulfonation. These solid acid catalysts, in the form of carbon spheres, were characterized through various techniques, including thermogravimetry, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy for elemental mapping (SEM-EDS), and Boehm titration. Two types of catalysts were produced through low-temperature hydrothermal carbonization. One catalyst underwent hydrothermal carbonization with the assistance of a catalyst, while the other was carbonized solely using water. The catalytic activity was assessed for up to the fifth reuse in the esterification reaction between oleic acid and methanol, employing 5% of the catalyst by mass, a 1-h reaction time at 100 °C, and a molar ratio of oleic acid to methanol at 1:12. The catalyst produced through hydrothermal carbonization in water demonstrated the best performance, with a conversion rate ranging from 91% to 88% over the five cycles, while the catalyst produced with the aid of a catalyst yielded conversion rates of 89%–82% over the same five cycles. Total acidity and sulfonic group acidity were calculated for each recycling of the aforementioned catalysts. As expected, catalytic activity was primarily influenced by the concentration of strong acid sites from the sulfonic groups, which decreased with each use of the catalyst. Scanning electron microscopy analysis confirmed that the removal of lignin from biomass residues increased the conversion of holocellulose into carbon spheres, and the functionalization with sulfuric acid did not disrupt the spherical structures of the catalysts. Thermogravimetric and differential thermogravimetric analyses showed that both hydrochars and catalysts possessed satisfactory thermal stability for use in sulfonation and esterification reactions, respectively. The TG-MS analysis allowed for the observation of the decomposition temperature of sulfur-containing gaseous emissions. FTIR and XPS confirmed the expected functional groups for hydrochars and biomass-derived catalysts. Moreover, XPS confirmed that the majority of sulfur present in the catalysts existed in the form of sulfonic groups. The optimization of reaction parameters, such as temperature, time, catalyst loading, and the molar ratio of oleic acid to methanol, was carried out using the catalyst with the best performance over the recycling cycles (91%–88%). By slightly increasing the values of these parameters in the esterification model reaction (5% catalyst by mass, 1-h reaction time at 100 °C, and a molar ratio of oleic acid to methanol of 1:12), oleic acid conversion between 89% and 93% was achieved. The utilization of açai seed-derived materials in this study showcases potential environmental benefits by reducing waste associated with açai seed commercialization. Additionally, these catalysts are considered green, as they are quick, cost-effective, and simple to produce, while exhibiting excellent catalytic activity and recyclability.

Incorporation of tin into zirconium phosphate to boost efficient conversion of trioses to lactic acid

Dihydroxyacetone isomerization is a fundamental reaction for the production of lactic acid using different feedstocks. However, achieving excellent catalytic activity and resistance against leaching in water is challenging. Herein, we devised a Sn doped zirconium phosphate as effective heterogeneous catalyst. The incorporation of Sn could remarkably aggrandize the content of strong Lewis acid sites while retain relatively high surface areas. Gratifyingly, this catalyst exhibits enhanced activity and reusability for selective dihydroxyacetone isomerization into lactic acid with water as solvent. High lactic acid yields of 70.30 and 76.25% were achieved in water and water/acetone under optimal reaction conditions, respectively. The composition and activity of catalyst are reserved with reduced ions leaching. The excellent catalytic performance is attributed to accelerated conversion of pyruvaldehyde to lactic acid by the strong Lewis acid sites. Nuclear magnetic resonance revealed that the reaction is proceeded via a keto-enol tautomerization process.

Boosting the low-temperature NH3-SCR performance via metals co-doping with inequality Mn/Ce ratios in the carbon-based catalyst prepared by Cr-containing leather waste

The resource utilization of Cr-containing leather waste is still a great challenge. In this work, waste from leather production as raw material was attempted to be used to synthesize activated carbon, a series of MnxCe1-xZr0.5/AC composite catalysts were prepared via loading three metal elements onto activated carbon by impregnation method, the NH3-SCR performance was measured in a low temperature range of 50 ∼ 200 °C. Among them, the catalyst Mn0.7Ce0.3Zr0.5/AC displays the optimal low-temperature SCR activity, excellent resistance to GHSV, H2O and SO2. The characterization results indicated that increasing the Mn/Ce inequality ratios within a certain range would promote the electron transfer between the active metal components, thereby enhancing the synergistic effect and the redox capacity of the catalysts, and it also could significantly improve the concentration of Lewis acid sites to accelerate the adsorption and activation of NH3, resulting in different catalytic activities. The in situ DRIFTS results prove that the Lewis acid site plays a vital role in the “fast SCR” reaction, and the whole reaction process conforms to the Langmuir-Hinshelwood (L-H) mechanism.