Selective catalytic reduction of NO by C2H2 over MoO3/HZSM-5

Molybdenum impregnated HZSM-5 zeolite catalysts with MoO₃ loading from 1 to 8 wt.% were studied in detail for the selective catalytic reduction (C₂H₂-SCR) of NO by acetylene. A 83.9% of NO could be removed by the reductant at 350 °C under 1600 ppm of NO, 800 ppm of C₂H₂ and 9.95% of O₂ in He over 2%MoO₃/HZSM-5 catalyst with a specific activity of in NO elimination and the competitiveness factor (c.f.) of 33.6% for the reductant. The NO elimination level and the c.f. value were ca. 3–4 times as high as those using methane or propene as reductant over the catalyst in the same reaction condition. About same reaction rate was estimated in NO oxidation as that in the NO reduction over each xMoO₃/HZSM-5 (x = 0–8%) catalyst, which confirms that NO₂ is a crucial intermediate for the aimed reaction over the catalysts. Appropriate amount of Mo incorporation to HZSM-5 considerably enhanced the title reaction, both by accelerating the intermediate formation and by strengthening the adsorption NO_x on the catalyst surface under the reaction conditions. Rather lower adsorption tendency of acetylene compared with propene on the catalysts explains the catalyst's steady performance in the C₂H₂-SCR of NO and rapid deactivation in the C₃H₆-SCR of NO.     

Non-oxidative reaction of CBrF3 with methane over NiZSM-5 and HZSM-5

Catalytic hydrodehalogenation of CBrF₃ with methane was studied over NiZSM-5 and HZSM-5 in tubular reactor between 573 and 873 K and at ambient pressure. It was found that the incorporation of nickel into HZSM-5 significantly enhanced the activity of the zeolite. A variety of products were formed during reaction, including CH₃Br, CHF₃, CH₂Br₂, C₂F₆, C₂H₄, C₂H₂, C₂H₂F₂, CHBrF₂, CH₂BrF, and C₂H₃Br. XRD analysis showed that these two zeolite catalysts did not suffer any loss in their crystallinity during use. Deactivation of both NiZSM-5 and HZSM-5 may, in part, be due to poisoning of the zeolite by halogens. Coking is another cause of the deactivation of HZSM-5, but appears to play a minor role in NiZSM-5 deactivation. A series of methylated silicone oils was detected during reaction over NiZSM-5.     

焙烧温度对HZSM-5分子筛催化1-丁烯齐聚性能的影响

考察焙烧温度对HZSM-5分子筛催化剂结构及1-丁烯齐聚性能的影响,采用XRD、SEM和NH3-TPD对催化剂进行表征。结果表明,升高焙烧温度,对HZSM-5分子筛催化剂的晶相和晶粒尺寸没有影响,催化剂中弱酸与强酸的酸强度和酸量均随焙烧温度的升高逐渐减弱。在催化剂晶粒尺寸一定条件下,催化剂酸性对催化剂的齐聚性能有较大影响,焙烧温度500℃时,C5+收率和C10+选择性最佳。     

全结晶ZSM-5分子筛催化剂研究及工业应用

制备了全结晶ZSM-5分子筛催化剂,采用XRD、SEM、N2物理吸附-脱附及NH3-TPD等对催化剂进行表征,并考察其用于碳四烯烃催化裂解制丙烯(OCC)反应的催化性能。结果表明,制备的全结晶ZSM-5分子筛催化剂比常规成型的催化剂具有更高的结晶度、更大的比表面积、更丰富的孔结构以及更多的活性中心。高空速有利于反应的进行,提高压力对反应不利,升高温度有利于提高产物丙烯收率。在实验室研究的基础上,将全结晶ZSM-5分子筛催化剂用于OCC工业装置,取得良好的应用效果。     

Surface properties and reactivity of Cu/γ-Al2O3 catalysts for NO reduction by C3H6: Influences of calcination temperatures and additives

The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al₂O₃ catalysts on the surface properties and reactivity for NO reduction by C₃H₆ in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al₂O₃ catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al₂O₃ and 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalysts calcined at 1073 K possess a CuAl₂O₄ phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C₃H₆ shows that the CuAl₂O₄ is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K, although these catalysts possess the same CuAl₂O₄ phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K is attributed to the formation of less active CuAl₂O₄ phase with high aggregation and preferential promotion of C₃H₆ combustion to CO_x by MnO₂. The engine dynamometer test for NO reduction shows that the C₃H₆ is a more effective reducing agent for NO reduction than the C₂H₅OH. The maximum reactivity for NO reduction by C₃H₆ is reached when the NO/C₃H₆ ratio is one.     

Conversion of naphthenes to a high value steamcracker feedstock using H-ZSM-5 based catalysts in the second step of the ARINO-process

Future regulations for the limitation of sulfur and aromatics in fuels driven by the European Auto Oil Program (AOP II) stimulate the need for an alternative utilization of the resulting surplus of pyrolysis gasoline (pygas). The conversion of heavy pyrolysis gasoline into valuable steam cracker feedstock with a maximum yield of C₂–C₄ n-alkanes is achieved via the ARINO^® two-step process, jointly developed by Linde, VEBA Oil and Süd-Chemie. The first step involves a hydrogenation of aromatics to naphthenes followed by the subsequent ring opening and cracking in the second step.

Süd-Chemie developed a new commercial cracking catalyst for the second step of the ARINO^® process with the aim to maximize the yield of C₂–C₄ n-alkanes at low formation of methane and aromatics. The ring opening and cracking reaction of naphthenes was studied in a bench scale tubular reactor over extruded H-ZSM-5 based zeolite catalysts.

In a series of screening tests using a commercial, hydrogenated and desulphurized heavy pyrolysis gasoline, the influence of the preparation parameters such as zeolite acidity, palladium content as well as the type of binder were investigated. Furthermore, the influence of the process conditions space velocity and temperature was studied.

High yields of C₂–C₄ n-alkanes at low formation of undesired methane and aromatics were achieved over an alumina bound zeolite with medium Brønsted acidity loaded with palladium.

The reduction of the space velocity resulted in an increase in the C₂–C₄ n-alkane yield and lower formation of aromatics, but a simultaneous increase in the methane make. Raising the temperature from 280 to 370 °C significantly increased the catalyst activity.     

Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

MgO/NaX zeolite as basic catalyst for oxidative methylation of toluene with methane

Oxidative methylation of toluene with methane was studied over a series of MgO/NaX zeolite catalysts. The effect of MgO on the zeolite was examined by X-ray diffraction (XRD) and temperature-programmed desorption (TPD) of CO₂. The results indicated that the conversion, selectivity and yield of C₈ hydrocarbons (ethylbenzene and styrene) are significantly improved by impregnation of maximum 13 wt.% MgO into the zeolite. The latter catalyst also displays a good stability. It is found that the amount of active sites but not their strength depends on the content of MgO in the zeolite. The catalysts possess well preserved crystal structure and low amount of MgO crystal phase.     

Fischer–Tropsch synthesis on monolithic catalysts of different materials

Monolithic structures made of cordierite, γ-Al₂O₃ and steel have been prepared as catalysts and tested for Fischer–Tropsch activity. The monoliths made of cordierite and steel were washcoated with a 20 wt.% Co–1 wt.% Re/γ-Al₂O₃ Fischer–Tropsch catalyst whereas the γ-Al₂O₃ monoliths were made by direct impregnation with an aqueous solution of the Co and Re salts resulting in a loading of 12 wt.% Co and 0.5 wt.% Re. The activity and selectivity of the different monoliths were compared with the corresponding powder catalysts.

Higher washcoat loadings resulted in decreased C₅₊ selectivity and olefin/paraffin ratios due to increased transport limitations. The impregnated γ-Al₂O₃ monoliths also showed similar C₅₊ selectivities as powder catalysts of small particle size (38–53 μm). Lower activities were observed with the steel monoliths probably due to experimental problems.     

Highly effective P-modified HZSM-5 catalyst for the cracking of C4 alkanes to produce light olefins

A series of HZSM-5 zeolites modified by different amounts of phosphorus (P/HZSM-5) were prepared. The physicochemical features of P/HZSM-5 catalysts were characterized by means of XRD, BET, NH₃-TPD, FT-IR spectra of adsorbed pyridine, etc., and their performances for the catalytic cracking of the mixed C₄ alkanes to produce light olefins were investigated. The results indicated that phosphorus (P) modification not only modulated the amount of acidic sites and the percentage of weak acidic sites in total acidic sites, but also regulated the acid type, i.e., the ratio of L/B (Lewis acid/Brönsted acid). The introduction of P also altered the basic characteristics of HZSM-5 which was evidenced by CO₂-TPD analysis. Consequently, P modification with suitable amount was favorable for enhancing the selectivity to light olefins, especially to propene. At the temperature of 650 °C, the maximum yields of propene and ethene were achieved 25.6 and 33.9%, which were higher than those over parent HZSM-5 by 7 and 4.5%, respectively. Aromatics yield was found to be decreased with the increasing P loading due to the reduction of strong acid and the formation of new basic site which inhibited the hydrogen transfer reaction. All this indicates that P-modified HZSM-5 zeolites are effective catalysts for the cracking of mixed C₄ alkanes to produce more light olefins.     

Cracking of n-heptane over Brønsted acid sites and Lewis acid Ga sites in ZSM-5 zeolite

A series of gallium-containing ZSM-5 zeolites prepared by wet impregnation, ion-exchange and chemical vapor deposition (CVD) methods are compared in the cracking of n-heptane. Impregnation results in the dispersion of some of the gallium oxide clusters into the zeolite pore network as charge-compensating Ga species after calcination. Reduction of impregnated Ga/HZSM-5 catalysts leads to complete transformation of the oxidic Ga precursors to charge-compensating Ga⁺ and GaH²⁺ species. A small amount of divalent GaH²⁺ species can be stabilized; however, with increasing Ga/Al ratio monovalent cations dominate. While a model Ga/HZSM-5 catalyst prepared by CVD of Ga(CH₃)₃ containing mainly charge-compensating Ga cations displays high selectivity to dehydrogenated products (olefins, toluene and coke), catalysts with a lower Ga/Al ratio display improved activity with a product mixture resulting from contributions of Ga sites (dehydrogenation, aromatization, olefin cracking) and of Brønsted acid sites (protolytic cracking, olefin cracking). The synergy between Ga dehydrogenation sites and Brønsted acid sites is proposed to improve the dehydrogenation rate: the high acidity of the zeolitic proton facilitates hydrogen recombination and concomitant removal of product olefin from the Ga active sites. Ion-exchanged Ga/HZSM-5 catalyst which combines a difficult to reduce gallium oxide phase and high Brønsted acidity has the highest activity with relatively weak coke formation.     

Catalytic coprocessing of LDPE with coal and petroleum resid using different catalysts

Catalytic coprocessing of low density polyethylene (LDPE) with coal and heavy petroleum resid was investigated using four different catalysts that included both hydrotreating and hydrocracking catalysts. Reaction systems that were evaluated included LDPE alone; LDPE with coal; and LDPE, coal, and resid. The catalysts used were NiMo/Al₂O₃, a hydrotreating catalyst with some hydrocracking activity, and the hydrocracking catalysts Zeolyst 753, NiMo/zeolite, and HZSM-5. These catalysts were reacted individually or in combinations of 10 wt.% of each hydrocracking catalyst in NiMo/Al₂O₃. The catalytic reactions were performed at two temperatures, 400 and 430°C, using 1 wt.% of each catalyst or a combination of catalysts on a total feed basis. The effects of the different catalysts on the reaction products were measured in terms of solvent fractionation and total boiling point distribution. Reactions at the higher reaction temperature of 430°C resulted in substantially higher conversion and production of lighter products than the reactions at 400°C. The LDPE reaction system was sensitive to the catalyst type, and yielded increased conversion and lighter products when Zeolyst 753 and NiMo/zeolite were used. By contrast, the conversion and product slate obtained from the LDPE and coal systems were low and showed no effect due to the different types of catalyst. Introduction of resid to the LDPE/coal system increased the reactivity of the system and allowed the catalysts to have a larger effect. The hydrocracking catalysts were the most active in producing more conversion and hexane soluble material. Comparison of the effect of increasing the reaction time up to 5 h with 1 wt.% catalyst loading to the effect of increasing the catalyst loading from 1 wt.% to 10 wt.% for a reaction time of 1 h showed that increased reaction time was much more effective than catalyst loading in converting the solid LDPE to liquid reaction products.     

Total oxidation of propene and propane over gold–copper oxide on alumina catalysts: Comparison with Pt/Al2O3

Oxidation of propene and propane to CO₂ and H₂O has been studied over Au/Al₂O₃ and two different Au/CuO/Al₂O₃ (4 wt.% Au and 7.4 wt.% Au) catalysts and compared with the catalytic behaviour of Au/Co₃O₄/Al₂O₃ (4.1 wt.% Au) and Pt/Al₂O₃ (4.8 wt.% Pt) catalysts. The various characterization techniques employed (XRD, HRTEM, TPR and DR-UV–vis) revealed the presence of metallic gold, along with a highly dispersed CuO (6 wt.% CuO), or more crystalline CuO phase (12 wt.% CuO).

A higher CuO loading does not significantly influence the catalytic performance of the catalyst in propene oxidation, the gold loading appears to be more important. Moreover, it was found that 7.4Au/CuO/Al₂O₃ is almost as active as Pt/Al₂O₃, whereas Au/Co₃O₄/Al₂O₃ performs less than any of the CuO-containing gold-based catalysts.

The light-off temperature for C₃H₈ oxidation is significantly higher than for C₃H₆. For this reaction the particle size effect appears to prevail over the effect of gold loading. The most active catalysts are 4Au/CuO/Al₂O₃ (gold particles less than 3 nm) and 4Au/Co₃O₄/Al₂O₃ (gold particles less than 5 nm).     

Potassium–copper and potassium–cobalt catalysts supported on alumina for simultaneous NOx and soot removal from simulated diesel engine exhaust

This paper deals with the activity of bimetallic potassium–copper and potassium–cobalt catalysts supported on alumina for the reduction of NO_x with soot from simulated diesel engine exhaust. The effect of the reaction temperature, the soot/catalyst mass ratio and the presence of C₃H₆ has been studied. In addition, the behavior of two monometallic catalysts supported on zeolite beta (Co/beta and Cu/beta), previously used for NO_x reduction with C₃H₆, as well as a highly active HC-SCR catalyst (Pt/beta) has been tested for comparison. The preliminary results obtained in the absence of C₃H₆ indicate that, at temperatures between 250 and 400 °C, the use of bimetallic potassium catalysts notably increases the rate of NO_x reduction with soot evolving N₂ and CO₂ as main reaction products. At higher temperatures, the catalysts mainly favor the direct soot combustion with oxygen. In the presence of C₃H₆, an increase in the activity for NO_x reduction has been observed for the catalyst with the highest metal content. At 450 °C, the copper-based catalysts (Cu/beta and KCu2/Al₂O₃) show the highest activity for both NO_x reduction (to N₂ and CO₂) and soot consumption. The Pt/beta catalyst does not combine, at any temperature, a high NO_x reduction with a high soot consumption rate.     

Direct synthesis of middle iso-paraffins from synthesis gas on hybrid catalysts

This paper focuses on the synthesis of iso-paraffin-rich hydrocarbons by Fischer–Tropsch synthesis (FTS) over silica gel supported Co catalyst (Co/SiO₂). The basic concept is to isomerize and/or hydrocrack the primary FTS hydrocarbon products. A physical mixture consisting of a small amount of zeolite or Pd/zeolite mixed with Co/SiO₂ enhanced the formation of C₄–C₁₀ iso-paraffins while suppressing the formation of higher molecular hydrocarbons, probably because of the selective cracking of these hydrocarbons on them. In separate experiments, a two-reactor system was used. The first reactor contained a physical mixture of Co/SiO₂ and zeolite, and the second reactor contained zeolites or Pd-supported zeolites. The two-reactor system gave sharp C-number distribution within C₃–C₆ and iso-paraffins-rich products. The hydrocracking of n-octane and n-decane (model compound simulating products of the FTS reaction) over mixed catalysts composed of various compositions of Pd/SiO₂ and ZSM-5 in the presence of gaseous hydrogen showed high and stable activity, and produced primarily iso-paraffin-rich hydrocarbons. The isomerization was favored for mixtures rich in Pd/SiO₂. The role of Pd was thought to be the inlet of hydrogen spillover to the zeolite surface.     

Hydro-thermal cracking of heavy oils and its model compound

Liquid-phase cracking of vacuum gas oil (VGO) was performed over NiMo supported nonacidic catalysts under 713 K and 8.0 MPa of hydrogen in a batch reactor, which is termed hydro-thermal cracking. Compared with VGO thermal cracking under the same reaction conditions the new process showed the suppressed naphtha yield (from 22.4 to 13.5 wt.%) and VGO conversion (from 65.7 to 64.0 wt.%) and increased the middle distillate yield (from 44.3 to 49.3 wt.%). At the same conversion level, the yield ratio of middle distillates to naphtha for this new process was two times higher than that for VGO hydrocracking. The VGO hydrocracking over USY-supported NiMo proceeded at much lower temperatures but gave higher naphtha yields. Both the thermal cracking and the hydro-thermal cracking of n-dodecyl benzene (C₆H₅(CH₂)₁₁CH₃) yielded toluene as the major aromatic product, whereas its hydrocracking over NiMo/USY yielded benzene as the major aromatic product. The reaction mechanism of this new process was assumed to consist of thermal cracking of hydrocarbon molecules via the free radical chain mechanism and the catalytic hydroquenching of free radicals.     

Lithium-doped sulfated-zirconia catalysts for oxidative coupling of methane to give ethylene and ethane

Li-doped sulfated-zirconia catalysts were found to be effective for oxidative coupling of methane (OCM). The catalyst performances depend on the sulfate content and calcination temperature. A maximum C₂ yield is attained over the catalysts, which contain 6 wt.% sulfate and calcined at 923–973 K, being closely related to the preparation conditions of sulfated-ZrO₂ as solid super-acids. When the performances of the Li-doped sulfated-ZrO₂ (Li/SZ) catalysts were tested at 1023 K as a function of reaction time, both the C₂ and CO_x selectivities remained constant over the range of 8 h, but the CH₄ conversion decreased from 17.5% to 11.9%. The nature of Li/SZ catalysts for the OCM was investigated by X-ray diffraction, XPS, and NH₃ and CO₂ TPD measurements. It could be postulated that the sulfated-ZrO₂ surface could play an important role in the formation of a catalytically active structure by Li-doping.     

Synergisms between matrices and ZSM-5 in FCC gasoline non-hydrogenating upgrading catalysts

This article describes a novel non-hydrogenating FCC gasoline upgrading catalyst system consisting of a kaolin/γ-Al₂O₃ binary-matrix and an active component zeolite HZSM-5. Different catalysts made from the different combinations of HZSM-5 with the three matrices (two kaolins and γ-Al₂O₃) or their binary mixtures were prepared and their catalytic performances were assessed in a continuously flowing fixed-bed reactor using FCC gasoline as feedstock. The results showed that compared with the single-matrix based HZSM-5 catalysts, the binary-matrix based HZSM-5 catalysts had much better catalytic performance. The characterization results of the acidity, specific area and pore structure properties of the catalysts revealed that the synergisms between the matrices and HZSM-5 in the acidity and pore distribution of the binary-matrix based catalysts accounted for their improved catalytic performance. Our results demonstrated that the non-hydrogenating catalyst system developed in the present investigation can convert olefins in FCC gasoline into aromatics that have higher research octane number (RON) and thus has potential application for FCC gasoline upgrading because of its excellent olefin reduction ability and RON preservability.     

Catalytic conversion of low-density polyethylene using a continuous screw kiln reactor

Both thermal and catalytic cracking of low-density polyethylene (LDPE) have been investigated using a screw kiln reactor. Thermal degradation gives rise to a broad product distribution, whereas catalytic cracking over Al-MCM-41 leads mainly to hydrocarbons within the gasoline range (C₅–C₁₂) with selectivities up to 80%. The increase of the screw speed between 3 and 15 rpm in the catalytic experiments allows the plastic feed rate to be varied in the range 20–41 g h⁻¹. The changes observed in the TOF values when varying the screw speed point out a decrease of the activity per site with increasing residence times, which may be due to the catalyst deactivation or to a contribution of the degradative extrusion at higher screw speeds. Likewise, a certain increase in the selectivity towards the gasoline fraction is observed at short residence times. On the other hand, PIONA analyses indicate that, regardless of the screw speed, the main components of the gasoline are olefins (50%) and isoparaffins (20%), whereas the aromatic content is always below 6%, with a proportion of benzene lower than 0.1%.     

Hydrocarbon synthesis through CO2 hydrogenation over CuZnOZrO2/zeolite hybrid catalysts

Direct syntheses of hydrocarbons from CO₂ hydrogenation were investigated over hybrid catalysts consisting of methanol synthesis catalyst (CuZnOZrO₂) and zeolites (MFI and SAPO). The yield of hydrocarbons was strongly depending upon the amount of zeolite's acid sites as measured by NH₃ TPD, while the product distributions were hardly affected by the change of acidity. The main product was ethane in the case of MFI hybrid catalyst and C₃ or C₄ hydrocarbon in the case of SAPO hybrid catalyst. This difference in product distribution was attributed to different mechanism of hydrocarbon formation. Investigation based on the ethene co-reaction suggested that the consecutive mechanism operated for HZSM-5 and the carbon pool mechanism for SAPO.