The catalytic dehydrogenation of cyclohexane and methylcyclohexane over nickel loaded Y zeolites

The dehydrogenation of cyclohexane to benzene and of methylcyclohexane to toluene was investigated over a range of nickel Y zeolites, varying the nickel content and the nature of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺). The overall reaction is viewed as occuring via a series of consecutive dehydrogenation steps. Catalytic activity is correlated with the reaction time, the reaction temperature, the level of Ni²⁺ exchange and the effects of pyridine adsorption. The level of dehydrogenation is strongly dependent on the mass of supported nickel metal and the surface Bronsted acidity. Catalyst deactivation results from the deposition of coke on the catalyst surface which is promoted with increasing zeolite acidity.     

Effect of doping with nickel and copper on catalytic behaviour of wide-pore zeolites with different pore structures

The catalytic properties of wide-pore zeolites, namely Ni- and Cu-doped faujastie H-Y and H-mordenite (H-M) are compared on the example of conversion of n-hexane. After thermal pretreatment of ion-exchanged zeolites, reduction with hydrogen (P ≤ 40 bar) leads to a large number of metallic clusters and crystallites as well as ionic species in the zeolites. Notwithstanding this variety, the different types of catalysts can be divided into three classes: classical bifunctional catalysts (for example NiHM, NiHY) with ion exchange degrees > 30%, monofunctional catalysts, such as CuHM and CuHY with high copper contents (ion exchange degree > 40%) and metal-doped (Ni and Cu) zeolites which, depending on the conditions of pretreatment, act as bifunctional and/or monofunctional compounds and, therefore, show very unstable reaction behaviour. In addition to the extent of reduction, the cation distribution affects the activity and deactivation behaviour and, to a lesser extent, the product selectivity. The reaction mechanism of bifunctional catalysis is similar to that observed in platinum-doped catalysts, while the mechanism of monofunctional catalysis resembles the process on undoped zeolites.     

The hydrogenation of toluene over nickel loaded Y zeolites

The catalytic activities of a range of hydrogen reduced nickel Y zeolites for the hydrogenation of toluene were measured and correlated with the following catalytic parameters: reaction temperature; reaction time; coke deposition. The role of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺) in influencing the overall hydrogenation activity of the supported nickel metal was probed. The effect of poisoning the surface Bronsted acidity by the adsorption of ammonia is discussed. For comparative purposes, data on the hydrogenation of benzene over the same catalysts are included.     

A catalytic and characterization study of the surface acidity generated on the reduction of copper exchanged Y zeolites

Zeolite acidity, in the form of Bronsted acid sites generated on reducing a range of copper Y zeolites, was probed by infrared spectroscopy. The nature of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) is shown to influence both the acid strength and location of the Bronsted sites. Acid strength decreases in the order CuLiY > CuNaY > CuKY > CuRbNaY > CuCsNaY. The specific effect of the alkali metal co-stations on the level of protonic activity in benzene ethylation and cumene cracking is discussed.     

Selective catalytic reduction of NO with propene over CuMFI zeolites: dependence on Si/Al ratio and copper loading

Selective catalytic reduction of nitrogen oxide by propene in an oxidising atmosphere was studied on several CuMFI catalysts with different Si/Al ratios (11 Si/Al 100) and different copper loadings (between 0 and 5.5 wt.-%). From the results it was observed that the influence of zeolite Si/Al ratio on CuMFI catalytic activity for NO SCR by propene is dependent on the catalyst copper loading. Furthermore, the effect of catalyst copper loading on catalytic performance depended on the catalyst Si/Al ratio. The results also demonstrated that CuMFI catalysts with different Si/Al ratios and copper loadings, but with the same Cu/Al ratio and, therefore, the same copper exchange level have similar catalytic activity profiles for NO SCR.

It was further observed that not all Cu cations exchanged into MFI catalysts have equivalent catalytic activity for NO SCR, which made the existence of different copper environments on CuMFI catalysts evident, isolated Cu²⁺ ions being the most active species for NO SCR by propene.

Moreover, the results showed an improvement of the CuMFI catalytic activity at low temperatures by increasing the catalyst copper exchange level and, consequently, decreasing the number of Brönsted acid sites, which can be performed either by increasing the zeolite Si/Al ratio or copper loading.     

铜渣载镍催化剂催化气化松木屑的实验研究

采用二级固定床管式反应器,以松木屑为原料,水蒸气为气化介质,载镍铜渣为催化剂,结合XRD、TEM、BET、SEM、H₂-TPR等表征手段,考察了不同的镍载量、催化剂焙烧温度以及催化温度对生物质催化气化的影响。结果表明,铜渣载镍催化剂有相对低的比表面积,但它表现出极好的抗积炭性能和裂解焦油的能力。镍载量为2.0%的催化剂经过600℃焙烧后,氢气产量为26.91mmol/g,碳转化率达到了94.86%,积炭仅为0.16%;当催化温度从850℃升高到900℃时,氢气产量只增加了0.28mmol/g,综合考虑能源消耗、催化性能以及设备损耗等因素,最佳的催化温度为850℃。由此可见,铜渣在镍催化剂上的应用可实现废物回收利用,有着重要的实用价值。     

Comparison of the product distribution in the catalytic cracking of dewaxed neutral distillate over lanthanum-exchanged X and Y type zeolites

A comparison of the selectivity for minor products formed from the same feedstock on LaX and LaY has shown that the two catalysts differ very little in their conversion of the feed. There is, however, a marked difference between the two catalysts in their activity toward short chain product olefins. These are rapidly saturated, cracked or turned to coke by the X catalyst.     

Oxidation of cyclohexane over copper phthalocyanines encapsulated in zeolites

The oxidation of cyclohexane to cyclohexanol, cyclohexanone and adipic acid has been studied using phthalocyanines and substituted (chloro- and nitro-) phthalocyanines of copper, cobalt and iron encapsulated in zeolites X and Y, at ambient conditions and using molecular oxygen as well as alkyl (tertiary butyl, cyclohexyl and cumyl) hydroperoxides as the oxidants. The catalytic efficiencies of the encapsulated materials are much higher than those of the neat complexes. The rate of oxidation of cyclohexane using copper hexadecachloro phthalocyanine- encapsulated Y zeolite catalysts is quite high (TOF=400 h^-1) with TBHP efficiencies which can reach upto 90%. The isolated encapsulated metal complex is the active site. Solvents exert a major influence on product distribution (cyclohexanol, cyclohexanone and adipic acid are the major products). Byproducts like succinic and glutaric acids are not formed when using acetonitrile as the solvent. Rates of oxidation when using the alkyl hydroperoxides as oxidants decrease with an increase in their molecular cross-section (cyclohexyl>t-butyl>cumyl) confirming that the active site is indeed located inside the zeolitic cavities and not on the external surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

空速对不同Y型分子筛FCC催化剂轻柴油裂化性能的影响

通过调节进料泵速,考察了空速对轻柴油在不同沸石含量的REUSY、REHY和REY型 FCC催化剂上裂化性能的影响。结果表明,随着空速的增加,原料在不同催化剂上转化率之间的差距逐渐增大,在低沸石含量的REY催化剂上转化率下降较缓,而在高沸石含量的REUSY催化剂上转化率下降较快。其原因可能在于低沸石含量的催化剂微孔总量较少,在高空速和短接触时间,受内扩散时间的影响小于高沸石含量的催化剂,因而表观裂化转化率较高     

The catalytic activity of Cu-ZSM-5 and Cu-Y zeolites in NO decomposition: dependence on copper concentration

NO decomposition was studied on Cu-ZSM-5 (Cu exchange extent from 23 to 210%) and Cu-Y (Cu exchange extent from 5 to 105%) catalysts at 773 K. The results show that the activity (NO molecules decomposed per gram of catalyst per second) increases by roughly 100-fold when the extent of exchange with copper in the ZSM-5 framework increases from 80 to 100%. This behaviour shows that not all Cu sites are equivalent in their decomposition activity. Cu-ZSM-5 samples prepared with either H-ZSM-5 or Na-ZSM-5 show the same activity pattern.     

Effect of hydrogen on discharge behaviour of the nickel oxide electrode

The effect of hydrogen on the discharge behaviour of the nickel oxide electrode has been investigated in 30% KOH solution at 25°C. Open-circuit potentials of the nickel oxide electrodes, previously fully charged, decrease more rapidly in a hydrogen atmosphere than in an argon environment. Voltammograms of the nickel oxide electrode show that the amount of cathodic charge decreases considerably when the nickel oxide electrode is exposed to hydrogen rather than to argon. These results, along with X-ray diffraction data, indicate that hydrogen can increase the self-discharge rate of the nickel oxide electrode as a result of reduction of -NiOOH to -Ni(OH)₂ and the simultaneous oxidation of hydrogen. In addition, hydrogen can produce changes in the nickel oxide electrode during charge that persist to modify discharge behaviour and open-circuit potential.     

硅源对Bi-MSU-4结构及催化性能的影响

分别以正硅酸乙酯、硅溶胶、硅酸钠和硅胶H为硅源,聚氧乙烯失水山梨醇软脂酸单酯（Tween-40）为模板剂,硝酸铋为铋源,合成出一种含铋的介孔分子筛Bi-MSU-4。采用X射线衍射（XRD）、紫外-可见光谱（UV-vis）和扫描电镜（SEM）对样品进行表征。并将所合成的Bi-MSU-4用于苯乙烯选择性反应中考察其催化活性。结果表明,硅源对Bi-MSU-4的结构和催化性能产生较大的影响。以正硅酸乙酯、硅酸钠为硅源,由于其水解速率缓慢,有利于分子筛的合成,所制得的样品相对结晶度和催化活性度较高;硅溶胶水解－聚合速率过快不能与模板剂完全作用,所制得的样品规整性较差,结晶度和苯乙烯的转化率都有所下降;酸性条件下不利于硅胶H的水解,反应体系中仍有硅胶H微粒的存在,从而大大影响其产物的结晶度和催化性能。     

Influence of synthesis method on the properties and catalytic performance of MCM-49 zeolites

Highly crystalline and pure MCM-49 was hydrothermally synthesized by dynamic and static methods, respectively. The properties of the samples were studied by N₂ adsorption, XRD, TEM and FT-IR techniques. The results indicated that MCM-49 synthesized by dynamic method showed much smaller crystal and lower concentration of acid sites. The Pd-supported catalyst on MCM-49 synthesized by static method showed higher acetone conversion in one-step synthesis of methyl isobutyl ketone from acetone, which was attributed to higher concentration of acid sites. While the higher selectivity to methyl isobutyl ketone for Pd-supported on MCM-49 synthesized by dynamic method might be related with the lower acidity and higher BET surface area.     

Improvement of toluene catalytic combustion by addition of cesium in copper exchanged zeolites

HY and HMFI zeolites exchanged with copper and cesium have been studied for the catalytic combustion of toluene (800 ppm) with air. The catalysts activity has been analyzed by comparison of light-off curves and in both Cu zeolites, the addition of Cs leads to a decrease of the light-off temperature by 50 °C. Temperature-programmed reduction (H₂-TPR) and EPR studies have evidenced clear differences in the characteristics of the copper species both in the presence and absence of Cs co-cations. These differences account for the nature of the active centers in the Cu zeolites for the toluene oxidation. The position and geometry of the copper ions in the zeolite matrix are of great significance for the redox behavior and activity for toluene oxidation. In both MFI and FAU structures, the bulky Cs co-cations are located in the more accessible main zeolite pores, forcing the copper ions to occupy the most stable, but less accessible positions within each structure. In the case of the MFI zeolite, the EPR study revealed that the Cs exchange resulted in an increased abundance in the number of square pyramidal Cu²⁺ ions relative to the other Cu environments. Cs co-cations also lead to an increase in the reducibility of the copper ions mainly due the reduction of protons in Cu, Cs-containing samples.     

Kinetic modeling of catalytic conversion of methylcyclohexane over USY zeolites: Adsorption and reaction phenomena

Catalytic conversion of cycloparaffins is a complex process involving competing reaction steps. To understand this process, FCC experiments using methylcyclohexane (MCH) on USY zeolite catalysts were carried out in the mini‐fluidized CREC riser simulator. Runs were developed under relevant FCC process conditions in terms of partial pressures of MCH, temperatures (450–550°C), contact times (3–7 s), catalyst‐oil mass ratios (5), and using fluidized catalysts. MCH overall conversions ranged between 4 to 16 wt %, with slightly higher conversions obtained using the larger zeolite crystallites. Moreover, it was found that MCH undergoes ring opening, protolytic cracking, isomerization, hydrogen transfer and transalkylation. A heterogeneous kinetic model for MCH conversion including thermal effects, adsorption and intrinsic catalytic reaction phenomena was established. Adsorption and kinetic parameters were determined, including the heat of adsorption (?40 kJ/mol), as well as thermal and primary catalytic intrinsic activation energies, which were in the range of 43–69 kJ/mol, and 50–74 kJ/mol, respectively. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Effects of metal modifications of Y zeolites on sulfur reduction performance in fluid catalytic cracking process

The acidity of catalytically active component, e.g., ultra stable Y zeolite (USY), plays an important role in determining their cracking activity and selectivity. To develop advanced sulfur reduction catalytic cracking catalysts, different type of elements were used to modify USY and the resulting catalysts were evaluated in a confined fluidized bed reactor and a micro-activity testing unit. The relation between the acidity of the zeolite and the conversion of sulfur compounds as well as the distributions of fluid catalytic cracking (FCC) products were discussed. The results showed that the rare earth (RE) metal can stabilize the catalyst and increase the conversion, but cannot increase the selectivity to thiophene compounds; V can reduce the sulfur content by 36.3 m%, but decreases the overall conversion compared with the base catalyst. An optimum catalyst was obtained by the combined RE and V modification, over which the sulfur content in FCC gasoline can be decreased and the selectivity for the target products can be improved, with the sulfur content reduced by 30 m% and the selectivity to coke even decreased by 0.20 m% at a comparable conversion level of the base catalyst.     

Oxidative dehydrogenation of n-butane over bimetallic mesoporous and microporous zeolites with CO2 as mild oxidant

Oxidative dehydrogenation of n-butane was tested using carbon dioxide as a mild oxidant over bimetallic Cr–V supported catalysts (MCM-41, ZSM-5, MCM-22 and mesoZSM-5). The textural properties of the catalysts were measured by means of XRD, N₂ adsorption, SEM-EDX, Raman, H₂-TPR, pyridine FT-IR, NH₃ and CO₂-TPD techniques. The metal content of Cr and V was maintained around 1.2 and 2.8 wt% for the catalytic test in packed bed reactor at different temperatures (525–600 °C) for 180 min. 1.2Cr2.8 V/MCM-41 and 1.2Cr2.8 V/ZSM-5 exhibited maximum conversion of 14 and 13.1 %, respectively at 10 min and 600 °C. Significantly, high butenes selectivity was observed over MCM-41 (86.27 %) than ZSM-5 support (58.1 %). The mesoporosity in ZSM-5 had a negative impact on conversion level (7.1 %) but improved the butenes selectivity slightly. 1.2Cr2.8 V/M-22 showed the highest cracking ability leading to overall reduced butenes selectivity (57.9 %). The study shows that over all catalysts, n-butane conversion is independent of CO₂ conversion. 1.2Cr2.8 V/M-22 showed highest CO₂ conversion in the range 2.35–2.2 % between 525 and 550 °C. The apparent activation energies of dehydrogenation and cracking reaction over the four catalysts were evaluated. The ratio of conversion to coke weight per cent over the four catalysts are observed in the following order: 1.2Cr2.8 V/M-41 > 1.2Cr2.8 V/Z-5 > 1.2Cr2.8 V/mesoZ-5 > 1.2Cr2.8 V/M-22.     

镍的沉积对催化剂活性及汽油性质的影响

利用ACE评价装置考察了镍沉积对催化裂化反应性能和汽油性质的影响。实验表明,镍在催化剂上沉积对催化剂中钠和稀土氧化物含量影响不大,但比表面积、孔体积和酸性降低,重油转化能力降低,干气和焦炭产率增加,汽油性质变差。     

镀液中氨基磺酸镍质量浓度对电镀镍层析氢催化活性的影响

采用由10 g/L NiCl₂·6H₂O、30 g/L NH₄Cl和310～390 g/L Ni(NH₂SO₃)2·4H₂O(氨基磺酸镍)组成的镀液(pH=3.8),在温度35°C和电流密度3 A/dm²的条件下电镀30 min,获得镍电极。研究了镀液中氨基磺酸镍质量浓度对镍镀层表面形貌和析氢催化活性的影响。结果表明,镀液中氨基磺酸镍质量浓度为350 g/L时,镍镀层结晶最细致,析氢催化活性和稳定性最佳。     

甲醇对噻吩在HZSM-5分子筛上转化反应的影响

在固定床微型反应器中,以HZSM-5（硅铝物质的量比为25）分子筛为催化剂,探讨了甲醇对噻吩催化脱硫转化反应的影响。实验表明,反应温度在350 ℃以上时,噻吩转化率达到51％以上;甲醇与溶剂苯的合适体积比为1∶2;负载于HZSM-5的氧化镧对噻吩的催化转化有较大的促进作用;负载氧化镧质量分数为1.0%时,噻吩的转化率和硫化氢的产率分别达到51.3％和18.1％,与母体HZSM-5分子筛催化剂相比,噻吩的转化率和硫化氢的产率分别提高了36.0％和11.9％;空速以14 h^-1为宜。