High Catalyst Loading Research Articles

Engineering of anchor sites and reaction time to efficiently synthesize high loading and stable sub-nanocluster catalysts

A series of sub-nanoclusters (M/C-X, M = Pt, Pd, Ru. C = KB, CNT, rGO. X = O, N, S) synthesized by engineering anchor sites and reaction time. These materials have an excellent catalytic effect on the hydrogen evolution reaction.

Organocopper(ii) complexes: new catalysts for carbon-carbon bond formation via electrochemical atom transfer radical addition (eATRA).

Organocopper(ii) complexes are a rarity while organocopper(i) complexes are commonplace in chemical synthesis. In the course of building a strategy to generate organocopper(ii) species utilizing electrochemistry, a method to form compounds with CuII–C bonds was discovered, that demonstrated remarkably potent reactivity towards different functionalized alkenes under catalytic control. The role of the organocopper(ii) complex is to act as a source of masked radicals (in this case ˙CH2CN) that react with an alkene to generate the corresponding γ-halonitrile in good yields through atom transfer radical addition (ATRA) to various alkenes. The organocopper(ii) complexes can be continuously regenerated electrochemically for ATRA (eATRA), which proceeds at room temperature, under low Cu loadings (1–10 mol%) and with the possibility of Cu-catalyst recovery.

Catalyst-free transesterification vitrimers: activation via α-difluoroesters

Transesterification vitrimers often require high catalyst loadings to prepare 3D networks reprocessable at moderately high temperature.

Suzuki−Miyaura coupling and O−arylation reactions catalysed by palladium(II) complexes of bulky ligands bearing naphthalene core, Schiff base functionality and biarylphosphine moiety

Schiff bases L1 [i.e., 2-(diphenylphosphino)-N-(naphthalen-1-ylmethylene)ethanamine], L2 [i.e., 2- (diphenylphosphino)-N-(naphthalen-2-ylmethylene)ethanamine], L3 [i.e., 2-(1-(2-(diphenylphosphino)ethylim- ino)ethyl)naphthalen-1-ol] and L4 [i.e., 2-((2-(diphenylphosphino)ethylimino)methyl)naphthalen-1-ol] have been synthesized using a straightforward methodology which involves a condensation reaction between H2N−CH2−CH2−PPh2 and appropriate carbonyl compound. Due to the presence of diphenylphosphine (−PPh2) moiety and >C = N− functionality, these compounds behave as ligands and undergo complexation reaction with palladium on treatment with Na2PdCl4 to yield the palladium(II) complexes (1–4). Ligands as well as complexes have been characterized using standard NMR spectroscopic techniques. ESI−MS and single crystal X−ray diffraction studies corroborate the structures of complexes. Crystal structures of complexes 1−3 reveal clearly that the geometry around Pd centre is distorted square planar. Ligands L1 and L2 are coordinated to Pd centre in bidentate (P, N type) mode, however, L3 and L4 act as a tridentate (P,N,O type) ligand and bind with metal in anionic mode. The Pd P and Pd N bond distances in complexes 1−3 are in the ranges 2.204−2.212 Å and 2.023−2.072 Å, respectively. Complex 3 [i.e., PdCl(L3−H)] also has a Pd-O bond, the length of which is found to be 2.009(3) Å. All the complexes have potential for catalysing O-arylation (C-O coupling) of phenol and Suzuki-Miyaura coupling (SMC) reactions. Both bromoarenes and chloroarenes can be used as substrates in Suzuki coupling and converted into biaryl derivatives. For O-arylation reactions of phenol, bromoarenes are used as arylating agents. For catalysis of such reactions (i.e., C-O coupling), high (0.1 mol%) catalyst loading is required. However, Suzuki reactions require low (0.001 mol%) loading of catalysts to occur with bromoarenes and give the products. The high potential of the complexes is also evident from the fact that they also convert different aryl chlorides into the coupled products in Suzuki coupling. 31P{1H} NMR data reveal that the electronic environments of nuclei of phosphorous donors are closely similar in all the four ligands. Similar magnitude of deshielding of the 31P{1H} signals in all the complexes indicate that, while forming the dative bond, the P donor of all the ligands transfer the electron density to the palladium to a similar extent. Hence, the electronic effects created by the ligands through the phosphorous donor are similar in all the complexes. Therefore, it is inferred that variation in their catalytic performance is because of difference in the binding mode of the ligand and/or minor alteration in the architecture of organic ligand. Amongst them, complex 2 shows the highest catalytic activity, and the least active catalyst is complex 3 for C-C coupling reactions. For C-O coupling reactions, the efficiencies of complexes 1 and 2 are slightly higher than those of complexes 3 and 4.

Accelerated SuFEx Click Chemistry For Modular Synthesis.

SuFEx click chemistry is a powerful method designed for the selective, rapid, and modular synthesis of functional molecules. Classical SuFEx reactions form stable S-O linkages upon exchange of S-F bonds with aryl silyl-ether substrates, and while near-perfect in their outcome, are sometimes disadvantaged by relatively high catalyst loadings and prolonged reaction times. We herein report the development of accelerated SuFEx click chemistry (ASCC), an improved SuFEx method for the efficient and catalytic coupling of aryl and alkyl alcohols with a range of SuFExable hubs. We demonstrate Barton's hindered guanidine base (2-tert-butyl-1,1,3,3-tetramethylguanidine; BTMG) as a superb SuFEx catalyst that, when used in synergy with silicon additive hexamethyldisilazane (HMDS), yields stable S-O bond linkages in a single step; often within minutes. The powerful combination of BTMG and HMDS reagents allows for catalyst loadings as low as 1.0 mol % and, in congruence with click-principles, provides a scalable method that is safe, efficient, and practical for modular synthesis. ASSC expands the number of accessible SuFEx products and will find significant application in organic synthesis, medicinal chemistry, chemical biology, and materials science.

Accelerated SuFEx Click Chemistry For Modular Synthesis**

AbstractSuFEx click chemistry is a powerful method designed for the selective, rapid, and modular synthesis of functional molecules. Classical SuFEx reactions form stable S−O linkages upon exchange of S−F bonds with aryl silyl‐ether substrates, and while near‐perfect in their outcome, are sometimes disadvantaged by relatively high catalyst loadings and prolonged reaction times. We herein report the development of accelerated SuFEx click chemistry (ASCC), an improved SuFEx method for the efficient and catalytic coupling of aryl and alkyl alcohols with a range of SuFExable hubs. We demonstrate Barton's hindered guanidine base (2‐tert‐butyl‐1,1,3,3‐tetramethylguanidine; BTMG) as a superb SuFEx catalyst that, when used in synergy with silicon additive hexamethyldisilazane (HMDS), yields stable S−O bond linkages in a single step; often within minutes. The powerful combination of BTMG and HMDS reagents allows for catalyst loadings as low as 1.0 mol % and, in congruence with click‐principles, provides a scalable method that is safe, efficient, and practical for modular synthesis. ASSC expands the number of accessible SuFEx products and will find significant application in organic synthesis, medicinal chemistry, chemical biology, and materials science.

Effects of CoMo/γ-Al2O3 Catalysts on Product Hydrocarbon and Phenol Distribution during Hydrodeoxygenation of Oxidized Bio-Oil in a Batch Reactor

Hydrodeoxygenation is an essential process for producing liquid transportation fuels. In this study, the effects of CoMo/γ-Al2O3 catalysts form and loading ratio on the hydrodeoxygenation upgrading of bio-oil were investigated in a batch reactor. Raw bio-oil was first oxidized with hydrogen peroxides and oxone to obtain the oxidized bio-oil with reduced levels of aldehydes and ketones, increasing the organic liquid yield during hydrodeoxygenation by suppressing the coke formation. CoMo/γ-Al2O3 was selected as the catalyst because of its low cost and commercial availability. The effect of the reduction and sulfidation of CoMo/γ-Al2O3 catalyst on the hydrodeoxygenation of the oxidized bio-oil was compared. The effect of the catalyst loading ratio on bio-oil hydrodeoxygenation using sulfided CoMo/γ-Al2O3 catalysts was also investigated. The research results showed that the sulfided CoMo/γ-Al2O3 catalyst facilitated the formation of hydrocarbons, while the reduced CoMo/γ-Al2O3 catalyst produced more phenols in the organic liquids. Moreover, a high sulfided catalyst loading ratio promoted the formation of hydrocarbons.

Black Tungsten Oxide Nanofiber as a Robust Support for Metal Catalysts: High Catalyst Loading for Electrochemical Oxygen Reduction (Small 47/2021)

Black Tungsten Oxide Nanofiber as a Robust Support for Metal Catalysts: High Catalyst Loading for Electrochemical Oxygen Reduction (Small 47/2021)

Black Tungsten Oxide Nanofiber as a Robust Support for Metal Catalysts: High Catalyst Loading for Electrochemical Oxygen Reduction.

Black valve metal oxides with low oxygen vacancies are identified to be promising for various industrial applications, such as in gas sensing, photocatalysis, and rechargeable batteries, owing to their high reducibility and stability, as well as considerable fractions of low-valent metal species and oxygen vacancies in their lattices. Herein, the nanofiber (NF) of black oxygen-deficient tungsten trioxide (WO3- x ) is presented as a versatile and robust support for the direct growth of a platinum catalyst for oxygen reduction reaction (ORR). The nonstoichiometric, poorly crystallized black WO3- x NFs are prepared by electrospinning the W precursor into NFs followed by their low-temperature (650 °C) reductive calcination. The black WO3- x NFs have adequate electrical conductivity owing to their decreased bandgap and amorphous structure. Remarkably, the oxygen-deficient surface (surface O/W = 2.44) facilitates the growth of small Pt nanoparticles, which resist aggregation, as confirmed by structural characterization and computational analysis. The Pt-loaded black WO3- x NFs outperform the Pt-loaded crystalline white WO3- x NFs in both the electrochemical ORR activity and the accelerated durability test. This study can inspire the use of oxygen-deficient metal oxides as supports for other electrocatalysts, and can further increase the versatility of oxygen-deficient metal oxides.

Glycerol Hydrogenolysis to Produce 1,2-Propanediol in Absence of Molecular Hydrogen Using a Pd Promoted Cu/MgO/Al2O3 Catalyst

The catalytic process of glycerol hydrogenolysis to produce 1,2-propandiol (1,2-PD) in the absence of external hydrogen addition has been investigated. The methanol present in the crude glycerol from a biodiesel production process is used to provide in situ hydrogen produced via methanol steam reforming for the glycerol hydrogenolysis process. This process can reduce the additional cost for the transportation and storage of molecular hydrogen and also reduce the safety risks related to using high hydrogen pressure. It was found that the introduction of Pd onto a Cu/MgO/Al2O3 catalyst significantly improved the glycerol conversion and 1,2-PD selectivity. The pseudo-first-order kinetic results suggested that the promoting effect of Pd is primarily attributed to the enhanced activity for the hydrogenation of acetol, which is the intermediate formed via glycerol dehydration. A 27−3 fractional factorial design experiment was carried out to investigate the impacts of seven single factors and their binary effects on two responses, namely 1,2-PD selectivity and glycerol conversion. The results showed that the glycerol feed concentration has the most significant effect on the 1,2-PD selectivity, such that the 1,2-PD selectivity is lower if a more concentrated glycerol is used as the feedstock; stirring speed, inert gas pressure and water to methanol molar ratio have insignificant effects on the reaction system. The addition of Pd, higher temperature and higher catalyst loading are the essential factors in order to obtain a high selectivity of 1,2-PD and a high glycerol conversion.

Total oxidation of carbon monoxide, VOC and reduction of NO2 with catalytic ceramic filter media

This paper deals with the effect of catalyst loading on the activity and selectivity of CuOx−MnOy catalysts on alumina-silicate supports (fiber material-Al2O3(44)/SiO2(56)). A special focus lies on the oxidation of CO, on mixtures of VOC from 1-butene, isobutane, n-butane, propane, ethene, and ethane, as well as on CO oxidation in the presence of NO2. The catalysts are prepared through wet impregnation of the filter section with an aqueous solution of copper and manganese nitrate. The rate of CO oxidation for small carbon monoxide concentrations of up to 1 vol.% is independent of catalyst loading in the filter material. In contrast, at a carbon monoxide concentration of around 3 vol.%, it is found that the rate of CO oxidation increased rapidly with increasing catalyst loading of the filter material. The highest catalytic activity of over 93% CO elimination is achieved at 290 °C for 1 vol.% CO and smaller catalyst loading and for 3 vol.% CO with higher catalyst loading. In long-term stability tests, complete CO conversion is measured without deactivating the catalyst at 390 °C for at least 100 h. The highest catalytic activity for VOC elimination of 90% is achieved in the temperature range of 350–420 °C. During the CONO2 reaction with and without O2, a constant decrease in the CO oxidation rate is observed, while the NO2 reduction rate remained constant at a temperature below 300 °C.

Platinum Nanowire Based Electrodes with Boosted Catalyst Utilization for Efficient Hydrogen Production in PEM Electrolyzer Cells

Due to the limited triple phase boundary (TPB) sites caused by the intrinsically low electrochemical active surface area (ECSA) of catalysts and poor interfacial contact between a catalyst layer and a porous transport layer, high noble metal catalyst loadings are generally required to achieve high-efficiency hydrogen production in low-temperature proton exchange membrane electrolyzer cells (PEMECs). Our recent studies have demonstrated that direct deposition of platinum nanoparticles onto 25-µm-thick titanium liquid/gas diffusion layers (LGDLs) can significantly reduce the cathode catalyst waste.1-3 To further lower the cost of both catalysts and electrode fabrication, for the first time, we develop a green chemical synthesis approach at room temperature to fabricate ultrathin electrodes composed of platinum nanowires (PtNW) in-situ grown on thin titanium LGDLs.4 Our developed high-speed micro-scale visualization system reveals that ultrathin Pt nanowires display more uniform reaction sites and favorable bubble detachment compared to conventional Pt nanoparticles. Impressively, when integrated into a PEMEC, the PtNW electrode with a low catalyst loading of 0.2 mg cm−2 can achieve a low cell voltage of 1.643 V and high efficiency of 90.08% at 1000 mA cm−2, which significantly surpasses conventional electrodes with high loadings. Such performance enhancement is mainly attributed to the high ECSA of catalysts, favorable hydrogen bubble detachment, and good conductivity of the whole electrode. References Z.Y. Kang, G.Q. Yang, J.K. Mo, Y.F. Li, S.L.Yu, D.A. Cullen, S.T. Retterer, T.J. Toops, G. Bender, B.S. Pivovar, J.B. Green Jr, and F.Y. Zhang. "Novel thin/tunable gas diffusion electrodes with ultra-low catalyst loading for hydrogen evolution reactions in proton exchange membrane electrolyzer cells." Nano Energy. 47, 434-441 (2018).J.K. Mo, Z.Y. Kang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green Jr, M.M. Mench, and F.Y. Zhang. “Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting.” Science Advances, 2, 1600690 (2016).Z.Y. Kang, J.K. Mo, G.Q. Yang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green Jr, M.M. Mench, and F.Y. Zhang. “Investigation of thin/well-tunable liquid/gas diffusion layers exhibiting superior multifunctional performance in low-temperature electrolytic water splitting.” Energy & Environmental Science, 10, 166-175 (2017).Z.Q. Xie, S.L. Yu, G.Q. Yang, K. Li, L. Ding, W.T. Wang, D.A. Cullen, H.M. Meyer III, S.T. Retterer, Z.L. Wu, P.X. Gao and F.Y. Zhang. "Ultrathin platinum nanowire based electrodes for high-efficiency hydrogen generation in practical electrolyzer cells." Chemical Engineering Journal. 410, 128333 (2021).

Brønsted Acid Catalyzed Stereoselective Polymerization of Vinyl Ethers.

Isotactic poly(vinyl ether)s (PVEs) have recently been identified as a new class of semicrystalline thermoplastics with a valuable combination of mechanical and interfacial properties. Currently, methods to synthesize isotactic PVEs are limited to strong Lewis acids that require a high catalyst loading and limit the accessible scope of monomer substrates for polymerization. Here, we demonstrate the first Brønsted acid catalyzed stereoselective polymerization of vinyl ethers. A single-component imidodiphosphorimidate catalyst exhibits a sufficiently low pKa to initiate vinyl ether polymerization and acts as a chiral conjugate base to direct the stereochemistry of monomer addition to the oxocarbenium ion reactive chain end. This Brønsted acid catalyzed stereoselective polymerization enabled an expanded substrate scope compared to previous methods, the use of chain transfer agents to lower catalyst loading, and the capability to recycle the catalyst for multiple polymerizations.

Less severe reaction conditions to produce levulinic acid with reduced humins formation at the expense of lower biomass conversion: Is it economically feasible?

Esters of levulinic acid constitute a promising class of renewable fuel additives that improve the cold properties of diesel and reduce soot emissions. However, the production of levulinic acid via thermolysis of biomass has low selectivity, a problem that compromises both yield and reactor operability, with impacts on cost. The main undesirable byproducts of this process are called humins, a dark insoluble residue. This work proposes and simulates an alternative reactor arrangement based on experimental results and analyzes reaction conditions via design of experiments to determine the factors that influence humins formation in the production of levulinic acid from sugarcane bagasse. Results indicate that a high residence time in hydrolysis increases humins formation, and a high temperature was found to deteriorate selectivity even further. Therefore, a high catalyst loading combined with low residence time and temperature is required to decrease losses. Considering the limitations of the simulated model, the conditions that minimize humins formation led to yields of 109 kg of furfural (from hemicelluloses) and 74 kg of levulinic acid (from cellulose) per dry tonne of sugarcane bagasse, with the production of 58 kg of humins. Results of economic analysis demonstrated that if humins disposal is associated with a high cost, low biomass conversion is required to yield a promising economic result, even though this might compromise the yield of levulinic acid and furfural. On the other hand, if value-added applications for humins become available, a similar conclusion applies if their production compromises reactor operability.

Paper mill sludge biochar to enhance energy recovery from pyrolysis: A comprehensive evaluation and comparison

Bio-oil and pyrolysis gas (py-gas) are two pyrolysis products available for potential energy recovery. Crude bio-oil, however, is typically corrosive and unstable, requiring special combustion equipment or catalytic upgrading to produce drop-in-grade fuel. In contrast, py-gas is readily useable in standard equipment for energy recovery. Previous research revealed that Ca-impregnated biochar catalyst improved bio-oil to py-gas conversion. Biochar produced from paper mill sludge (p-sludge) has very high Ca content. In this study, the catalytic ability of p-sludge biochar was systematically evaluated for the first time in pyrolysis. P-sludge biochar resulted in higher py-gas yield (40 wt% of total pyrolysis products) and py-gas energy (8400 kJ of py-gas per biosolids pyrolyzed) than other biochar catalysts (e.g. wood and corn stover biochars) and mineral catalysts (e.g. calcined dolomite). Under some conditions (e.g. high temperature and catalyst loading), catalysis completely eliminated the nonaqueous phase condensate. A lower catalyst-to-feedstock ratio was required using p-sludge biochar compared to other biochars for similar performance. P-sludge biochar also had a longer catalyst lifetime based on the effectiveness over five reuse cycles. Bio-oil catalyzed by p-sludge biochar contained fewer organic constituents based on GC-MS and GC-FID analyses (e.g. toluene, ethylbenzene, styrene, phenol, cresol, and indole were not identified after catalysis).

Radical Cyclization of 1,n-Enynes and 1,n-Dienes for the Synthesis of 2-Pyrrolidone.

2-Pyrrolidones have aroused enormous interest as a useful structural moiety in drug discovery; however, not only does their syntheses suffer from low selectivity and yield, but also it requires high catalyst loadings. The radical cyclization of 1,n-enynes and 1,n-dienes has demonstrated to be an attractive method for the synthesis of 2-pyrrolidones due to its mild reaction conditions, fewer steps, higher atom economy, excellent functional group compatibility, and high regioselectivity. Furthermore, radical receptors with unsaturated bonds (i. e. 1,n-enynes and 1,n-dienes) play a crucial role in realizing radical cyclization because of the ability to selectively introduce one or more radical sources. In this review, we discuss representative examples of methods involving the radical cyclization of 1,n-enynes and 1,n-dienes published in the last five years and discuss each prominent reaction design and mechanism, providing favorable tools for the synthesis of valuable 2-pyrrolidone for a variety of applications.

Maximizing light olefins and aromatics as high value base chemicals via single step catalytic conversion of plastic waste

Chemical recycling of plastic waste via thermochemical processes is essential to move to a carbo-circular economy, reducing our dependence of fossil resources. However, recovering monomers from polyolefins in one or multiple steps is challenging due to their chemical inertness. In the present work, a tandem micro-pyrolyzer coupled to comprehensive two-dimensional gas chromatography and FID/ToF-MS detectors was utilized to study the performance of industrial formulations of steam-treated FCC catalysts and HZSM-5 additives for the in-line catalytic upgrading of polyolefin pyrolysis products towards light olefins and aromatics in two steps. When upgrading pyrolysis vapors from LDPE over the steam-treated catalysts at 600 °C, CH4 yields did not exceed 0.5 wt% due to their low acidity. The FCC catalyst formulations obtained higher yields of C5-C11 aliphatics (up to 42 wt%) and were more active in converting C12 + products than the HZSM-5-containing additives. The highest C2-C4 olefin selectivity of 53 wt% was obtained using a bare steam-treated HZSM-5 additive. With this catalyst, at higher catalyst loading and temperature (700 °C), the light olefin yield reached 69 wt% (19% ethylene, 22% propylene, 10% 1,3-butadiene, and 18% other C4 olefins). Importantly, similar yields of light olefins with even higher propylene yields of 31 wt% were obtained when processing real post-consumer mixed polyolefin waste. An adjusted loading of unsteamed catalyst (to obtain a similar level of initial conversion of C12 + products) showed higher coking propensity and deactivated more rapidly than its steam-treated version. The research results show great potential for the pyrolysis of mixed polyolefin waste followed by the direct in-line upgrading of the pyrolysis vapors to produce high value base chemicals such as C2-C4 olefins, aromatics, and naphtha-range aliphatics at high selectivity while limiting formation of coke, CH4, and H2.

Redox‐Mediated Ambient Electrolytic Nitrogen Reduction for Hydrazine and Ammonia Generation

AbstractThis work presents a redox‐mediated electrolytic nitrogen reduction reaction (RM‐eNRR) using polyoxometalate (POM) as the electron and proton carrier which frees the TiO2‐based catalyst from the electrode and shifts the reduction of nitrogen to a reactor tank. The RM‐eNRR process has achieved an ammonium production yield of 25.1 μg h−1 or 5.0 μg h−1 cm−2 at an ammonium concentration of 6.7 ppm. With high catalyst loading, 61.0 ppm ammonium was accumulated in the electrolyte upon continuous operation, which is the highest concentration detected for ambient eNRR so far. The mechanism underlying the RM‐eNRR was scrutinized both experimentally and computationally to delineate the POM‐mediated charge transfer and hydrogenation process of nitrogen molecule on the catalyst. RM‐eNRR is expected to provide an implementable solution to overcome the limitations in the conventional eNRR process.

Ir-catalyzed asymmetric hydrogenation of ketones using novel PNO phosphine ligands

<p indent=0mm>The asymmetric hydrogenation of ketones continue to be a hot research topic because of the importance of secondary chiral alcohols in the production of pharmaceuticals and many other products. For example, based on the asymmetric hydrogenation of ketones, our group has synthesized Duloxetine and Ezetimibe, which were important and best selling antidepressant and antihyperlipidemic drugs. On the other hand, phosphine ligands were found to be the critical factor to increase the activity of metal catalysts. Thus, since the successful application of BINAP by Noyori and co-workers, hundreds of phosphine ligands have been developed for the more efficient transformation of ketones into chiral alcohols. For example, BPE ligand reported by Burk group in 1993, Miniphos ligand synthesized by Imamoto and coworkers in 1999, series of SDP ligands developed by Zhou group since 2002, were both efficient and successful ligands for the asymmetric transformation of different ketones. Since 1997, our group also contributed many improved ligands for this reaction, such as, Binapine, f-amphox, et al. Despite significant achivements, there are still some questions to be solved in this area. For example, the synthesis of needed ligands demands hash reaction conditions and expensive starting materials, and sometimes the purification of the corresponding ligands was hard. Thus, new ligands or new synthetic methods are still in need for the more efficient transformation. Recently, we got interested in the introduction of prolinols as building blocks for the modification of ligands to control the enantioselectivity of this transformation. As a class of commercial available chiral building blocks, prolinol and its derivatives were increasingly applied as ligands or additives in the controls of enantioselectivity of organic transformations. In this context, combining our long standing interests in the developing of ferrocene based ligands, we designed and synthesized some novel PNO type phosphine ligands through three simple steps. Notably, the applied starting materials for these ligands were both commercially available chiral building blocks. The corresponding ligands have the advantages of easily available starting material, convenient synthesis, and simple purification. With these ligands in hand, we tested their catalytic activity on Ir-catalyzed asymmetric hydrogenation of acetophenone, which gave 99% conversion and high ee value of the product. Encourage by these positive result, we further optimized the reaction conditions including the solvent, base species, H₂ pressure, and the catalyst loading. THF was the best solvent among the test solvents. Since most of the tested base species giving similar results, we assumed base has only slight effect on both the conversion of acetophenone and the enantioselectivity of corresponding product. In some additional reaction conditions screening experiments, we found that a higher H₂ pressure or a higher catalyst loading was favorable for the conversion of acetophenone and the enantioselectivity of corresponding product. Thereafter, various different ketones were tested using the optimal reaction conditions. This catalytic system was compatible well with halides substitutions, methoxy gourps, and -CF₃ gourps, and also possible for the application in the transformation of heterocycles. Herein, an efficient and practical protocol was developed for the asymmetric hydrogenation of ketones. The proposed catalytic system gave the corresponding chiral secondary alcohols in up to >99% yield, 99% ee, and 100000 TON. In view of the high efficiency and easy synthesis of the ligand, we assume this work has remarkable potential regarding industrial process in the near future.

Persulfate activation by reduced graphene oxide membranes: Practical and mechanistic insights concerning organic pollutants abatement

The catalytic activity of membranes produced with commercial unmodified reduced graphene oxide (rGO) was demonstrated for the first time in persulfate (PS) activation through experiments performed in continuous mode. Phenol (Ph; C0 = 5 mg L−1) and venlafaxine (VFX; C0 = 250 µg L−1) were employed as model compounds. The influence of the main operation parameters was first investigated considering an operation period of 24 h. For a rGO membrane with an effective area of 2.1 cm2, contaminant removal is favored at lower flow rates (0.1 mL min−1) and higher catalyst loads (15 mg). Assays carried out under these conditions yielded average removals of 90 and 94% for Ph and VFX, respectively, corresponding to normalized removal rates in the range of 1.71–1.79 L m−2 h−1 mgcat−1. Membrane stability tests were conducted in continuous mode for 1 week, allowing to observe a significant catalyst deactivation after 2–3 d of operation, although the catalytic activity could be recovered through simple thermal regeneration procedures. Batch mode oxidation tests employing powder rGO treated at different temperatures (500, 850 and 1000 °C) and materials characterization data allowed to conclude that a shift of the surface chemistry character from acidic to basic enhances the catalytic performance. Moreover, scavenging tests indicated that singlet oxygen (1O2), apparently generated by nucleophilic attack of PS to C = O in pyrone-like functionalities, is the main oxidizing species in the rGO-PS system.