Double-bond isomerization of n-butenes over silicon-modified aluminophosphate molecular sieve catalysts: Reaction characteristics and influence of pore size on stereoselectivity

Double-bond isomerization of n-butenes was studied over silicoaluminophosphate molecular sieve structures SAPO-5, SAPO-31, and SAPO-11 at normal pressure within the temperature range 420–510 K. Kinetic measurements verified that (i) the reaction is acid-catalyzed, (ii) the respective isomers are interconvertible, and (iii) the reaction is of first order regarding but-1-ene up to partial pressures of about 12 kPa. Steady-state activities do not correlate with the concentration of Brönsted acid sites detectable on the fresh catalysts owing to the different resistance of the molecular sieve structures against deactivation. Stereoselectivity of the reaction, i.e., the ratio of cis-but-2-ene to trans-but-2-ene is influenced by the pore size of the molecular sieves, leading to lower percentages of cis-but-2-ene with decreasing pore diameters (SAPO-5 > SAPO-31 > SAPO-11).     

Acidity and acid strength distribution of the crystalline microporous MAPO-36 molecular sieve

n situ i.r. acidity measurements of MAPO-36 show the presence of Brönsted and Lewis acid sites. The temperature-programmed desorption spectra of pyridine, obtained by the mass spectrometric technique, over MAPO-36, AIPO₄-5, and SAPO-5 reveal the presence of the two types of acid sites. At a comparable concentration of the substituted element (Si or Mg) in the aluminophosphates of types 5 and 36, the concentration of Brönsted acid sites is significantly higher in MAPO-36. The results of temperature-programmed desorption and stepwise thermal desorption of pyridine (using g.c. techniques) indicates that MAPO-36, SAPO-5, and AIPO₄-5 respectively) above 673 K indicate the substitution of Mg²⁺ for some of the Al³⁺ in the aluminophosphate framework of type 36.     

Hydroisomerization and hydrocracking of n-hexane on Pt/SAPO-5 and Pt/SAPO-11 catalysts

The activity, stability, and selectivity of a series of bifunctional Pt/SAPO-5 and Pt/SAPO-11 catalysts containing 0.5 wt% platinum, were compared for n-hexane transformation at 300–425°C and atmospheric, 3- and 5-bar hydrogen pressures. Hydrogen pressure had a strong influence on the activity, isohexane selectivity, and time-on-stream deactivation. Isomerization to isohexanes was the major reaction in both cases. However, Pt/SAPO-5 shows high activity and higher isohexane selectivity than Pt/SAPO-11 catalyst. The selectivity patterns found in this class of molecular sieve catalysts are well interpreted in terms of a series of reaction pathways incorporating both confinement effects and shape selectivity factors as being important in determining the observed product distribution.     

Cerium-based coordination polymers micro/nanostructures: Room temperature synthesis and their thermolysis to ceria

In this presentation, several cerium-based coordination polymers micro/nanostructures such as nanoparticles, nanorods, and microflowers were successfully prepared by a facile room temperature method using three isomers of benzenedicarboxylic acid as organic building block and Ce³⁺ as center metal ion. It turns out that the three products exhibit obviously different morphologies. Also, their crystal structures are different. Amorphous products were obtained when benzene-1,2-dicarboxylic acid was used. However, well-crystallized products were obtained with the other two isomers. After calcining at high temperature, ceria with retained morphologies were achieved. Various measurements were used to characterize the products and their UV absorption properties were studied.     

Ultrafine Nanoparticle‐Supported Ru Nanoclusters with Ultrahigh Catalytic Activity

The design of an ideal heterogeneous catalyst for hydrogenation reaction is to impart the catalyst with synergetic surface sites active cooperatively toward different reaction species. Herein a new strategy is presented for the creation of such a catalyst with dual active sites by decorating metal and metal oxide nanoparticles with ultrafine nanoclusters at atomic level. This strategy is exemplified by the design and synthesis of Ru nanoclusters supported on Ni/NiO nanoparticles. This Ru‐nanocluster/Ni/NiO‐nanoparticle catalyst is shown to exhibit ultrahigh catalytic activity for benzene hydrogenation reaction, which is 55 times higher than Ru–Ni alloy or Ru on Ni catalysts. The nanoclusters‐on‐nanoparticles are characterized by high‐resolution transmission electron microscope, Cs‐corrected high angle annular dark field‐scanning transmission electron microscopy, elemental mapping, high‐sensitivity low‐energy ion scattering, and X‐ray absorption spectra. The atomic‐scale nanocluster–nanoparticle structural characteristics constitute the basis for creating the catalytic synergy of the surface sites, where Ru provides hydrogen adsorption and dissociation site, Ni acts as a “bridge” for transferring H species to benzene adsorbed and activated at NiO site, which has significant implications to multifunctional nanocatalysts design for wide ranges of catalytic reactions.     

Study on the mechanism of NH3-selective catalytic reduction over CuCexZr1--<?Pub Caret?>x/TiO2

Copper--cerium--zirconium catalysts loaded on TiO₂ prepared by a wet impregnation method were investigated for NH₃-selective catalytic reduction (SCR) of NO_x. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH₃ is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe_0.25Zr_0.75/TiO₂ at high temperature, while Br?nsted acid sites are more important than Lewis acid sites at low temperature. For the NH₃+NO+O₂ co-adsorption, NH₃ species occupy most of activity sites on CuCe_0.25Zr_0.75/TiO₂ catalyst, and mainly exist in the forms of NH₄⁺ (at low temperature) and NH₃ coordinated (at high temperature), playing a crucial role in the NH₃-SCR process. Two different reaction routes, the L-H mechanism at low temperature (<200°C) and the E-R mechanism at high temperature (>200°C), are presented for the SCR reaction over CuCe_0.25Zr_0.75/TiO₂ catalyst.     

Synthesis of SAPO-11 and AIP04-11 molecular sieves in the presence of Cu(ll)

The possible incorporation of Cu(II) into SAPO-11 (CuSAPO-11) and AIPO₄-11 (CuAPO-11) by adding Cu(II) compounds during synthesis in the presence of di-n-propylamine or diisopropylamine templates has been assessed. The location of Cu(ll) is identified by electron spin resonance and electron spin echo modulation spectroscopies. Cu(ll) ions do not incorporate into framework positions of SAPO-11 and AIPO₄-11, i.e., Cu(II) in CuSAPO-11 is located in the same position as Cu(ll) introduced byaqueous ion-exchange and Cu(ll) in CuAPO-11 is located in an extraframework position of AlPO₄-11. It is of ancillary interest that in the presence of Cu(ll) the SAPO-5 phase can be obtained as a major product by varying the temperature and time of crystallization.     

Fabricating Single‐Atom Catalysts from Chelating Metal in Open Frameworks

In the present study, a highly efficient strategy is reported using open framework platforms with abundant chelating ligands to fabricate a series of stable metal single‐atom catalysts (SACs). Here, the metal ions are initially anchored onto the active bipyridine sites through postsynthetic modification, followed by pyrolysis and acid leaching. The resulting single metal atoms are uniformly distributed on a nitrogen‐doped carbon (N‐C) matrix. Interestingly, each metal atom is found to be coordinated with five N atoms, in contrast to the average coordination number of four as previously reported. The as‐prepared Fe SAC/N‐C catalyst exhibits excellent oxygen reduction reaction (ORR) activity (with a half‐wave potential of 0.89 V), outstanding stability, and good methanol tolerance. The density functional calculations reveal that the coordinated pyridine can favorably modulate the interaction strength of oxygen on the Fe ion and thus improve the ORR activity. More importantly, it is demonstrated that this strategy can be successfully extended to the preparation of other transition metal SACs, simply by altering the metal precursors used in the metalation step.     

The acidic properties of SAPO-37 compared to faujasites and SAPO-5

SAPO-5 and two samples of SAPO-37 are compared to HY, LZY-82, and a dealuminated HY with regard to the hydroxyl properties and interactions with pyridine to form pyridinium ions. The three SAPO's have a higher thermal stability of their hydroxyls than do the faujasites. The two samples of SAPO-37 show a Brönsted acidity as strong as that of the dealuminated faujasites. The number of acid sites is expressed by that of SiOAl species, which allows a comparison to be made with the SiAl zeolites. The measurement of the number of sites is difficult because of an interaction of pyridine with some OH groups—not neutralizing them, but very likely shifting the HF band to low wavenumbers as benzene does. Partial regeneration of hydroxyl groups can be carried out on a SAPO-37 material rehydrated after a pretreatment at 1093 K.     

Ultrafine Metallic Nickel Domains and Reduced Molybdenum States Improve Oxygen Evolution Reaction of NiFeMo Electrocatalysts

An electrocatalyst for oxygen evolution reaction (OER) is essential in the realization of renewable energy conversion technologies, but its large overpotential, slow charge transfer, and degradation of surface reaction sites are yet to be overcome. Here, it is found that the metallic nickel domains and high‐valence reduced molybdenum ions of NiFeMo electrocatalysts grown on a 3D conductive and porous electrode without using binders enable ultrahigh performance in OER. High resolution‐transmission electron microscope and extended X‐ray absorption fine structure analyses show that metallic nickel domains with Ni–Ni bonds are generated on the catalyst surface via a dry synthesis using nitrogen plasma. Also, Mo K‐edge X‐ray absorption near‐edge spectroscopy reveals that Mo⁶⁺ ions are reduced into high‐valence modulating Mo⁴⁺ ions. With the metallic nickel domains facilitating the adsorption of oxygen intermediates to low‐coordinated Ni⁰ and the Mo⁴⁺ pulling their electrons, the catalyst exhibits about 60‐fold higher activity than a Mo‐free NiFe catalyst, while giving about threefold faster charge transfer along with longer stability over 100 h and repeated 100 cycles compared to a bare NiFeMo catalyst. Additionally, these metallic domains and high‐valence modulating metal ions are exhibited to give high Faradaic efficiency over 95%.     

Incorporation of mixed metals into SAPO-34 frameworks by the dry-gel conversion method using mixed templates: investigating catalysts characterisation and performance

The crystallisation of the MeAPSO-34 material was studied under dry-gel conversion conditions and using two and three templates. This study has been focused on the effect of the incorporation of a mixture of Ni and Mn into the SAPO-34 framework. The MeSAPO-34 samples were characterised by X-ray diffraction, energy-dispersive X-ray spectrometer, scanning electron microscope, temperature-programmed desorption and Brunner–Emmett–Teller. The influence of metal incorporation into the framework of SAPO-34 (MeAPSO-34) on methanol conversion was investigated in this study. The performances on methanol conversion for these catalysts were different according to the properties of metals incorporated into the SAPO-34 structure. The catalytic performance demonstrated high activity and light olefins selectivity for the prepared catalysts. Among the light olefin products, Mn and Ni incorporation is helpful for propylene generation, but samples with a mixture of Ni and Mn favour the ethylene production.     

Distinction of Leu and Ile Using a Ruthenium(II) complex by MALDI-LIFT-TOF/TOF-MS analysis

The novel N-terminal labeling method using a ruthenium(II) complex derivative characteristically indicated a(n) and d(n) (N-terminal) fragment ions in high sensitivity by MS/MS analysis (MALDI-LIFT or ESI-CID). Although these fragment ions depended on a fragmentation process by MS/MS analytical methods to some degree, each case indicated similar side-chain cleavage patterns. The labeling method allows accurate distinction of amino acid residues by MS/MS analysis even if the residues are structural isomers such as leucine and isoleucine. The method was applied to long-chain peptides and provided easy and rapid N-terminal sequencing.     

Synthesis and characterization of a basic molecular sieve: Nitrogen-incorporated SAPO-34

Microporous nitrogen-incorporated SAPO-34 molecular sieves were synthesized by thermal post-treatment of SAPO-34 in flowing dry ammonia at elevated temperatures. The results of property characterized by DRIFTS of CO₂ adsorption and CO₂–TPD showed that basic sites existed on the surface of nitridized samples probably due to the presence of nitrogen-containing species incorporating into the framework of SAPO-34 molecular sieves. The changes in structure of nitrogen-incorporated samples were investigated by ²⁷Al MAS NMR, ³¹P MAS NMR spectra X-ray diffraction and BET surface area measurements. It was found that nitrogen-incorporated SAPO-34 still kept good crystallinity and high specific surface area of precursors. And N-containing species had incorporated into the framework of samples during nitridation, in which N atom presumably bounded to Al and P atoms formed N-containing groups, but unfortunately some of them were not ascribed.     

氮化硼纳米片负载纳米Cu2O及其催化还原对硝基苯酚

纳米级氧化亚铜具有高效的催化性能, 但较差的稳定性使其应用受限。本研究采用简单可控的抗坏血酸液相还原及气氛焙烧法, 制备了一种兼具高催化活性与催化稳定性的Cu₂O/BNNSs-OH负载型催化剂, 其中以聚乙烯吡咯烷酮(PVP)与水相变提供的“推-拉”作用剥离的氮化硼纳米片(BNNSs)为载体, 液相还原反应体系pH=11时, 抗坏血酸向Cu ²⁺滴定制备的Cu₂O纳米颗粒(2~7 nm)为活性组分。通过扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、原子力显微镜(AFM)、X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、傅里叶变换红外光谱仪(FT-IR)及拉曼(Raman)光谱仪等对样品的形貌和结构进行表征, 结果表明: Cu₂O纳米粒子不但高度分散于载体表面, BNNSs对Cu₂O还有一定的稳定作用, 避免其被氧化成CuO。将Cu₂O/BNNSs-OH应用于对硝基苯酚催化还原反应中, 该催化剂表现出同贵金属类似的高催化活性, 5次重复利用后的转化率仍高达90%。     

Cu/Fe双金属负载PAN非织造布催化降解甲醛气体研究

采用偕胺肟改性聚丙烯腈(PAN)非织造布作为载体材料,将其与Cu~(2+)和Fe~(3+)的混合溶液进行反应制备双金属负载PAN非织造布催化剂。采用XPS和UV-Vis对催化剂的分子结构进行了表征,然后考察了其在甲醛气体氧化降解反应中的催化作用。结果表明,Cu~(2+)和Fe~(3+)均是通过与偕胺肟基团中的羟基和氨基的配位作用负载于PAN非织造布上,而且两种金属离子可能通过配体发生了相互作用。此外,与Fe~(3+)的单金属催化剂相比,适量掺杂Cu~(2+)能够有效提高催化体系在甲醛降解反应中的催化活性,尤其有利于其在暗反应时催化降解甲醛气体,这主要归因于Cu~(2+)/Cu~+价态转化促进了强氧化性中间体Fe(Ⅳ)=O的生成。     

X-ray diffraction and solid-state n.m.r. studies of AEL molecular sieves: Effect of hydration

Interpretation of X-ray powder diffraction spectra by using profile refinement techniques allowed the determination of (i) the positions of P, Al and O atoms in AEL-type materials (AlPO₄-11, SAPO-11) and (ii) the effect of adsorbed water molecules on the geometry of the previously evacuated AEL framework. The as-synthesized sample (hereafter labeled SYN form) and the 550°C calcined form (CAL form) crystallize in the acentric Ima2 space group with 3P + 3Al sites per asymmetric unit, whereas the rehydrated material (WAT form) adopts the acentric Pna2₁ space group with 5P + 5Al sites per asymmetric unit.In MAS-n.m.r. spectroscopy, a broad ³¹P peak observed for the SYN and the dehydrated CAL forms is centered near δ = −30.7 ppm and is interpreted as the evelope of three overlapping components with 2:1:2 intensity ratios (8P1:4P2:8P3). For the hydrated WAT form two peaks centered at δ = −23 and −29 ppm having an intensity ratio of 1:4 have been attributed to the 4P1 and the 4P2 + 4P3 + 4P4 + 4P5 sites, respectively. The first peak corresponds to the P1 species, which is attached to OH and/or water molecules, as shown by proton cross-polarization experiments. The second broad peak, which corresponds to the remaining P atoms, is interpreted as four overlapping peaks of equal intensity. Water molecules were shown by X-ray diffraction experiments to form dimeric clusters and to be located close to P1 in the elliptical channels. It is suggested that this atom could be substituted by Si atoms in the SAPO-11 samples, as supported by the observed 1:4 intensity ratio and by the fact that the intensity of the component corresponding to P1 decreases with increasing Si content.     

高产量制备石墨烯及其优异的重金属离子检测性能

以氧化石墨的高温膨胀为基础,研发了一种简便经济的高产量制备石墨烯的工艺,考察了制备得到的石墨烯对痕量重金属离子的检测性能,检测离子包括Cu2+、Pb2+和Cd2+.所制薄层石墨烯存在部分结构缺陷和残余羟基官能团,电化学检测结果表明,这种结构的石墨烯在检测液相中重金属离子的过程中表现出了很好的性质,尤其是对铅离子的检测限...     

Atmospheric pressure covalent adduct chemical ionization tandem mass spectrometry for double bond localization in monoene- and diene-containing triacylglycerols

We report a method to elucidate the structure of triacyl-glycerols (TAGs) containing monoene or diene fatty acyl groups by atmospheric pressure covalent adduct chemical ionization (APCACI) tandem mass spectrometry using acetonitrile as an adduct formation reagent. TAGs were synthesized with the structures ABB and BAB, where A is palmitate (C16:0) and B is an isomeric C18 monoene unsaturated at position 9, 11, or 13 or an isomeric diene unsaturated at positions 9 and 11, 10 and 12, or 9 and 12. In addition to the species at m/z 54 observed in previous CI studies of fatty acid methyl esters, we also found that ions at m/z 42, 81, and 95 undergo covalent reaction with TAGs containing double bonds to yield ions at m/z 40, 54, 81, and 95 units greater than that of the parent TAG: [M + 40]+, [M + 54]+, [M + 81]+, and [M + 95]+ ions. When collisionally dissociated, these ions fragment to produce two or three diagnostic ions that locate the double bonds in the TAG. In addition, ions [RCH=C=O + 40]+ and [RCH=C=O + 54]+ formed from collisional dissociation are of strong abundance in MS/MS spectra, and collisional activation of these ions produces two intense confirmatory diagnostic ions in the MS3 spectra. Fragment ions reflecting neutral loss of an sn-1-acyl group from [M + 40]+ and [M + 54]+ are more abundant than those reflecting neutral loss of an sn-2-acyl group, analogous to previous reports for protonated TAGs. The position of each acyl group on the glycerol backbone is thus determined by the relative abundances of these ions. Under the conditions in our instrument, the [M + 40]+ adduct is at the highest signal and also yields all information about the double bond position and TAG stereochemistry. With the exception of geometries about the double bonds, racemic TAG isomers containing two monoenes or dienes and a saturate can be fully characterized by APCACI-MS/MS/MS.     

Accurate mass-driven analysis for the characterization of protein phosphorylation. Study of the human Chk2 protein kinase

We describe the data-dependent analysis of protein phosphorylation using rapid-acquisition nano-LC-linear quadrupole ion trap Fourier transform ion cyclotron resonance mass spectrometry (nano-LC-FTMS). The accurate m/z values of singly, doubly, and triply charged species calculated from the theoretical protonated masses of peptides phosphorylated at all Ser, Thr, or Tyr residues of the human checkpoint 2 (Chk2) protein kinase were used for selected ion extraction and chromatographic analysis. Using a kinase-inactive Chk2 mutant as a control, accurate mass measurements from FTMS and collision-induced dissociation spectra, 11 novel Chk2 autophosphorylation sites were assigned. Additionally, the presence of additional Chk2 phosphorylation sites in two unique peptides was deduced from accurate mass measurements. Selected ion chromatograms of all Chk2 phosphopeptides gave single peaks except in three cases in which two closely eluting species were observed. These pairs of phosphopeptides were determined to be positional isomers from MS/MS analysis. In this study, it was also found that ions due to the neutral loss of phosphoric acid from the parent peptide ion were not prominent in 18 of 36 MS/MS spectra of O-linked Chk2 phosphopeptides. Thus, accurate mass-driven analysis and rapid parallel MS/MS acquisition is a useful method for the discovery of new phosphorylation sites that is independent of the signature losses from phosphorylated amino acid residues.     

利用含有模板剂的SAPO-34分子筛制备高效铜基催化剂

氮氧化物污染已经成为一个严重的环境问题。利用分子筛催化剂进行选择性催化还原(SCR)处理氮氧化物是最有效的方法之一。为了降低现有催化剂的制备成本, 本工作直接利用含有模板剂的分子筛浆料为原料, 通过预处理、离子交换及一次焙烧的方法制备Cu-SAPO-34催化剂。采用XRD、BET、TG、ICP、XPS、SEM、TPR、TPD及NH₃-SCR等对制备的Cu-SAPO-34样品进行表征, 并对离子交换过程中的pH条件进行了优化。研究结果表明: 利用含模板剂的分子筛浆料制备得到催化剂含有2.43% Cu、立方晶型完整、酸性较强以及催化还原性能优秀。在200~450℃下, NO转化率超过80%, 并且在300℃时转化率达到最高97.8%。与使用商品化SAPO-34制备的催化剂相比, 两者具有相似的微观结构和SCR性能。SAPO-34分子筛中少量模板剂的存在对最终制备得到的Cu-SAPO-34催化剂的性能影响很小。因此采用含有模板剂的分子筛浆料制备高效Cu-SAPO-34催化剂是可行的。