Remarkable enhancement in durability of Pd/H-ZSM-5 zeolite catalysts for CH4-SCR

Effect of second components on the catalytic performance of Pd/H-ZSM-5 zeolite (Pd: 0.4 wt.%) was evaluated by a durability test of NO reduction with CH₄ at a relatively high temperature of 500°C in the presence of water vapor for a prolonged period. The Pd/H-ZSM-5 showed high stable activity for this reaction without H₂O in the reactant feed, while immediate and irreversible deactivation was observed in the presence of H₂O, resulting in no activity after 7 h. The second components such as Co, Rh, Ag, Ce, and Fe introduced individually to the Pd/H-ZSM-5 enhanced the durability, and in particular the addition of 3.3 wt.% Co led to a stable NO conversion for more than 40 h in the presence of H₂O.     

Heat-treatment of isomorphously substituted ZSM-5 (MFI) zeolites An ESR and Mössbauer spectroscopy and kinetic study

Fe-ZSM-5 zeolites comprise of three types (I, II and III) of iron (Fe³⁺) sites in both as synthesized (AS) and heat-treated states. Previous evidence could be confirmed by the assignment of ESR lines, registered in the X-band, stating: (i) type I framework Fe³⁺ sites (in T_h oxygen coordination), where charge compensation occurs mainly by Na⁺ ions and the crystal field (cf) approximates cubic symmetry, produce resonances at near to g = 2.00; (ii) type II and probably type III binuclear Fe...Fe dioxo- and oxo-bridges manifest themselves in producing slightly distorted surroundings of axial symmetry, and the relevant powder-averaged subspectrum is superimposed on the previous one in the g  2.45–1.98 interval. As the temperature of the heat-treatment (HT) is raised, type II and III sites will be annihilated with preference, under concomitant production of amorphous Fe₂O₃ possessing molecular dispersity. (iii) The weak ESR signal (2–4%) at g  4.27 is attributed to T_h coordinated framework sites in the surface layers (≈ 1 u.c. thick) under the influence of solid surface tension, giving rise to fully rhombic cf symmetry.

The size of the ejected Fe₂O₃ particles, as estimated from Mössbauer spectra (no hyperfine structure at 77 K) is less than 2.9 nm. The extremely large electron affinity of Fe³⁺ ions manifests itself in decreased ionicity (and unexpectedly dominant cubic symmetry), activity in biomimetic oxidations, autoreduction and spontaneous reoxidation etc.

In the liquid phase oxidation by hydrogen peroxide of n-hexane and cyclohexane the heat-treated Ti-ZSM-5 samples exhibited both activity- and selectivity dependence on HT. On the basis of experiences drawn from the heat-treatments proposal is made for the structures of the defect site (producing the 960 cm⁻¹ IR signal) and the active centre of selective oxidation. The proposal seems to be in accord with the experimental observations (isotopic exchange, MAS-NMR behaviour etc.) published so far.     

国内外碳五资源利用综述

介绍了国内外Ｃ５资源分离及利用现状,对内Ｃ５资源综合利用提出初步建议．     

Reduction of NOx over Fe/ZSM-5 catalysts: mechanistic causes of activity differences between alkanes

Fe/ZSM-5 catalysts prepared by sublimation of FeCl₃ onto H/ZSM-5 catalyze the selective reduction of NO_x by hydrocarbons to N₂. The order of the relative rates and N₂ yields obtained with different alkanes reveals a non-trivial chemistry. The maximum yield is lower for propane than for n-butane but about the same for n- and iso-butane. However, at temperatures below this maximum, the N₂ yield is higher for propane and n-butane than for iso-butane. Deposits are formed on the catalyst that contain N atoms in a low-oxidation state which are able to react with NO₂ to form N₂. TPO and FTIR results show that the amount and also the character of the deposits depend on the nature of alkanes. The change of the oxidation state of nitrogen from a high value in NO or NO₂ to a lower value in nitrile and amino groups of the deposit is rationalized by applying mechanistic concepts of organic chemistry, including the Beckmann rearrangement and fragmentation. FTIR spectra and the observed oxygen- and nitrogen-containing compounds by GC-MS are potential clues to the reaction mechanism.     

Mc5—Ⅰ锻钢工作辊的研制

通过对有色铝板轧机后段工作辊的研制,开发了一种适应中等硬度中间辊及有色轧机工作辊的新型轧辊用材料。     

5A06电子束焊接Mg元素烧损规律及对接头力学性能的影响

研究了5A06合金电子束焊接时,熔池内Mg元素的分布规律以及Mg元素烧损对焊接力学性能的影响。结果表明：在接头区域,越靠近热影响区的Mg元素烧损程度越低;随着焊缝深度的增加。Mg无素烧损程度减小,同时显微硬度增大,烧损程度越严重的试样显微硬度越低。     

Study on the Components and Performance of GCrlS Bearing Steel Surface by Gas Multi-elements Penetrating

GAS multi-elements penetrating technology is a newsurface hardening technology developed on the basisof carbonitriding technology.It can not only shortenthe production period,but also improve the mechanicalperformances of the parts,such as torsional strength,flexural strength,wear resistance,and fatigue resistance"'.It features low-temperature multi-elementspenetration that the physical chemistry process ofoxidation-reduction generates the active atoms in thepart surface.In the beginning,the …     

Laser Cladding of an Al-11.7Wt%Si Alloy on ZM5 Magnesium Alloy to Enhance the Corrosion Resistance

MG and its alloys are widely used in aerospace andautomotive in industry.Its poor corrosion resistancerestricts application of Mg alloy.Laser cladding andlaser surface melting are advantageous processes forimprovement of the corrosion resistance of themagnesium alloy[1-2].In the present study,lasercladding of an Al-11.7Wt%Si alloy with two differentthickness on ZM5die cast alloy was performed withCC>2laser with different powder thickness.1.Experimental ProcedureDie cast plates of ZM5Mg a…