Coking and regeneration of palladium-doped H3PW12O40/SiO2 catalysts

The coking during propene oligomerisation and subsequent regeneration of both silica-supported heteropoly acid H₃PW₁₂O₄₀ (PW) and its palladium-modified form (1.6–2.5 wt% Pd) have been studied. ³¹P MAS NMR studies have revealed that the Keggin structure of the catalyst was unaffected by coke deposition in both unmodified PW/SiO₂ and Pd-modified form. As shown by ¹³C MAS NMR and TGA/TPO, the Pd modification affects the nature of the coke formed: for the standard catalyst (PW/SiO₂) both soft coke, comprising mainly high molecular weight aliphatic oligomers, and hard coke, comprising polynuclear aromatics, are formed whilst on the Pd-modified catalyst only the soft coke is observed. Coke formation causes strong deactivation of the catalyst in the oligomerisation of propene. The aerobic burning of coke on the unmodified PW/SiO₂ occurs in the temperature range of 470–520°C. Doping the catalyst with Pd significantly decreases this temperature to allow catalyst regeneration at temperatures as low as 350°C without loss of catalytic activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of La2O3 promoter on the structure of MnOx/SiO2 catalysts

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses have been used to characterize the structure of a La₂O₃-promoted MnO_x/SiO₂ catalyst, before and after its utilization in the oxidative dehydrogenation of ethylbenzene (EB). MnO_x/SiO₂ and MnO_x/La₂O₃/SiO₂ catalysts were prepared by pore volume impregnation, using aqueous solutions of (i) La³⁺-nitrate at an atomic ratio of La/Si = 0.08, and (ii) Mn²⁺-nitrate at an atomic ratio of Mn/Si = 0.10, followed by drying and calcination at 500°C in air. XRD data show no diffraction patterns specific to MnO_x on the La₂O₃-promoted MnO_x/SiO₂ catalyst, after calcination. Thus, the presence of La₂O₃ apparently favors the dispersion of manganese oxides during calcination, presumably by forming mixed Mn-La oxides. On the fresh promoted and unpromoted catalysts, after calcination, XRD and XPS analyses indicated that Mn was present mostly as MnO₂ and Mn₂O₃. In the used catalyst, Mn from the unpromoted catalyst degenerated from Mn⁴⁺ to Mn²⁺, resulting in formation of Mn₃O₄ species, whereas in the case of La₂O₃-promoted catalyst Mn remained well dispersed as MnO₂ and Mn₂O₃. It appears that La₂O₃ precludes the formation of Mn₃O₄ during the EB dehydrogenation, conserving Mn structure and oxidation state. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ethenolysis of esters of vegetable oils: Effect of B2O3 addition to Re2O7/SiO2.Al2O3-SnBu4 and CH3ReO3/SiO2.Al2O3 metathesis catalysts

Impregnation of SiO₂.Al₂O₃ (24.3% Al₂O₃ with 6% B₂O₃ increases the activity of supported Re₂O₇ in the ethenolysis of methyl oleate, but reduces the activity of CH₃ReO₃ on the same support. Re₂O₇/SiO₂.Al₂O₃/B₂O₃-SnBu₄ is shown to be an effective catalyst for the ethenolysis of methyl linoleate and of the methyl esters of olive oil, and can be recycled after calcination at least five times without loss of activity.     

Preparation and characterization of WO3/SiO2 catalysts

Two sets of WO₃/SiO₂ catalysts were prepared from (NH_{4 6}H₂W₁₂O₄₀ (aqueous method) and W(³-C₃H₅)₄ (non-aqueous method). The molecular structures and dispersions of the surface tungsten oxide species for the WO₃/SiO₂ catalysts under ambient and in situ dehydrated conditions were investigated by Raman spectroscopy. The samples prepared from (NH₄)₆H₂W₁₂O₄₀ (aqueous method) exhibit very strong Raman features due to the presence of crystalline WO₃ and the samples prepared from W(³-C₃H₅)₄ (non-aqueous method) do not possess crystalline WO₃. These results suggest that the preparation method exerts an influence on the dispersion of the surface tungsten oxide species on SiO₂. The surface tungsten oxide species under ambient conditions possess polytungstate clusters, W₁₂O ₄₂ ^12– , on the silica support. Upon dehydration at elevated temperatures, the hydrated polytungstate clusters decompose and interact with the silica support via the formation of isolated, octahedrally coordinated tungsten oxide species.     

CuO/SiO_2-Al_2O_3/堇青石催化剂选择性还原NO_X性能研究

采用溶胶-凝胶法制备了不同硅铝配比的CuO/SiO2-Al2O3/堇青石催化剂,通过XRD、BET、XPS等手段对催化剂进行表征,对尿素选择性还原氮氧化物(SCR)的行为进行了研究。结果表明,500℃焙烧后的复合涂层,随着SiO2含量的增加,其物相组成从单纯γ-Al2O3演化为无定形态SiO2与γ-Al2O3晶相共存,比表面积从47.30 m2/g增大到70.25 m2/g。150~400℃范围内的活性测试表明,当温度为250℃,SiO2/Al2O3比为1∶2时,催化剂活性最大为67.0%。     

载体焙烧温度对Ni/SiO2-Al2O3催化剂稳定性的影响

为了获得高水热稳定的负载Ni催化剂,延长催化剂在含水液相体系中的使用寿命,以不同温度焙烧的SiO₂-Al₂O₃为载体,采用浸渍法制备Ni/SiO₂-Al₂O₃催化剂,通过吡啶-原位傅立叶变换红外光谱、X射线衍射、NH₃-程序升温脱附和H₂-程序升温还原等方法进行表征,以水相1,4-丁炔二醇加氢为探针反应,研究载体焙烧温度对Ni/SiO₂-Al₂O₃催化剂催化加氢性能及含水体系中稳定性的影响。结果表明,在(400~800) ℃,随着载体焙烧温度升高,活性组分Ni存在状态及催化剂加氢活性变化较小,但催化剂的水热稳定性下降,造成这一现象的原因是随着载体焙烧温度升高,载体表面SiO₂聚集,暴露的Al³⁺增加,载体水合程度增大。载体焙烧温度400 ℃时,Ni/SiO₂-Al₂O₃催化剂表现出最佳的水热稳定性。     

Effect of Au in V2O5/SiO2 and MoO3/SiO2 catalysts on physicochemical and catalytic properties in oxidation of C3 hydrocarbons and of CO

Silica supported vanadia and molybdena catalysts with, and without Au, were prepared, characterized with XRD, TEM, XPS, H₂-TPR and probe reaction of isopropanol decomposition, and tested in the oxidation of propene, propane and CO. The presence of Au: (a) does not affect markedly structural and textural properties, such as specific surface area, size of V₂O₅ or MoO₃ crystallites, or the electronic state of V and Mo ions, (b) increases the reducibility of vanadia and molybdena phase, (c) enhances the dehydrogenation properties in isopropanol decomposition, and (d) modifies catalytic activity in oxidation reactions. The Au particles increase the total activity in CO oxidation. For propane oxidation at high temperatures the increase in total activity is observed, with the decrease in the selectivity to oxidative dehydrogenation product (propene) and increase in the selectivity to CO₂. The catalytic performance in propene oxidation at 200–300 °C depends on the Au presence and the composition of the reaction mixture. The gold-containing catalysts favour allylic oxidation of propene to acrolein and oxyhydration to acetone, and suppress the C₂ products (ethanal, acetic acid) of partial degradation of a propene molecule. In the presence of hydrogen in the reaction mixture, higher selectivities of acetone (product of oxyhydration) were observed for all the catalysts.     

The molecular structures and reactivity of V2O5/TiO2/SiO2 catalysts

A series of V₂O₅/TiO₂/SiO₂ catalysts were structurally investigated byin situ Raman spectroscopy and chemically probed by methanol oxidation in order to determine the molecular structure-reactivity relationships of the V₂O₅/TiO₂/SiO₂ catalysts. Only surface TiO _x species are present on the 3% TiO₂/SiO₂ catalysts, and the surface TiO _x species as well as bulk TiO₂ (anatase) particles coexist on the 40% TiO₂/SiO₂ catalyst. The deposition of 1–3% vanadium oxide onto 3% TiO₂/SiO₂ and 4% vanadium oxide onto 40% TiO₂/SiO₂ forms only a surface vanadium oxide phase.In situ Raman studies reveal that the surface vanadium oxide species preferentially exist on the titania sites of the TiO₂/SiO₂ system. The interaction between the surface vanadia and the surface titania overlayer on SiO₂ increases the methanol oxidation reactivity by two orders of magnitude relative to V₂O₅/SiO₂. In the presence of bulk TiO₂ (anatase) particles on the SiO₇ support, the reactivity of the surface vanadia further increases by an order magnitude relative to the catalysts containing only surface titania, and is close to that of surface vanadia on bulk TiO₂. This suggests that the surface VO _x -TiO₂ (bulk) interactions results in a more active site than the surface VO _x -TiO _x -SiO₂ interactions. In addition, the V₂O₅/TiO₂/SiO₂ catalysts exhibit high selectivity towards HCHO because redox sites are predominant on the surface of these catalysts with essentially no acid site present.     

Pulse studies of CH4 interaction with NiO/Al2O3 catalysts

Pulse studies of the interaction of CH₄ and NiO/Al₂O₃ catalysts at 500°C indicate that CH₄ adsorption on reduced nickel sites is a key step for CH₄ oxidative conversion. On an oxygen-rich surface, CH₄ conversion is low and the selectivity of CO₂ is higher than that of CO. With the consumption of surface oxygen, CO selectivity increases while the CO₂ selectivity falls. The conversion of CH₄ is small at 500°C when a pulse of CH₄/O₂ (CH₄O₂=21) is introduced to the partially reduced catalyst, indicating that CH₄ and O₂ adsorption are competitive steps and the adsorption of O₂ is more favorable than CH₄ adsorption     

Gas-phase hydrogen-transfer reduction of acrolein using 2-propanol over MgO/B2O3 and SiO2/AlPO4 catalysts

Two MgO/B2O3 and SiO2/AlPO4 catalysts designated BM50 and PM2, respectively, were used in the gas-phase hydrogen transfer between acrolein and 2-propanol to obtain allyl alcohol and propanal. The acid-base properties and catalytic activity of the two systems were found to be rather different. Thus, the MgO/B2O3 catalyst is more selective towards allyl alcohol than is the SiO2/ AlPO4 catalyst (conversion to the alcohol was 28% with the former and 0% with the latter). This special selectivity is discussed in terms of the different ways in which acrolein can be adsorbed on the catalytic surface as revealed by temperature-programmed desorption profiles and DRIFT spectra for pre-adsorbed acrolein. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Al2O3/SiO2 ratio on iron-based catalysts for Fischer–Tropsch synthesis

A systematic study was undertaken to investigate the effects of Al₂O₃/SiO₂ ratio on reduction, carburization and catalytic behavior of iron-based Fischer–Tropsch synthesis (FTS) catalysts promoted with potassium and copper. The catalysts were characterized by N₂ physical adsorption, CO₂ temperature-programmed desorption (TPD), H₂ temperature-programmed reduction (TPR) and Mössbauer effect spectroscopy (MES). CO₂-TPD indicated that Al₂O₃ binder has stronger acidity than SiO₂ binder and weakens the surface basicity of the catalysts. H₂-TPR profiles suggested that the lower Al₂O₃/SiO₂ ratio promotes the reduction of Fe₂O₃→Fe₃O₄. With further increasing Al₂O₃/SiO₂ ratio, the transformation of Fe₂O₃→Fe₃O₄ shifts to higher temperatures. The MES results showed that the increase of Al₂O₃/SiO₂ ratio leads to the relatively large crystallite size of α-Fe₂O₃ and inhibits carburization of the catalyst. During reaction tests in a fixed bed reactor it was found that a maximum in catalyst activity is noted at the Al₂O₃/SiO₂ ratio of 5/20 (weight basis). The selectivity to olefins shows a rapid decrease and the formations of methane and light hydrocarbons are promoted with increasing Al₂O₃/SiO₂ ratio. The oxygenate selectivity in total products increases with increasing Al₂O₃/SiO₂ ratio.     

Propylene metathesis over Re2O7/Al2O3-B2O3 catalysts

A series of alumina aluminum borate (AAB) with various Al/B molar ratios were prepared by the coprecipitation method. The supported rhenium oxide catalysts with various contents of Re₂O₇ were also prepared by the impregnation method with perrhenic acid. The catalytic activity and stability of Re₂O₇/AAB catalysts for the reaction of propylene metathesis were tested in a fixed-bed microreactor. It was found that Re₂O₇/AAB is more active, stable and regenerable than Re₂O₇/Al₂O₃ for propylene metathesis. The optimum Al/B molar ratio was found to be in the range of 4–10.     

钒系脱氮催化剂载体堇青石的表面改性研究

采用硅溶胶对堇青石蜂窝陶瓷载体进行表面改性,并在改性载体基础上制备钒系催化剂。考察了扩孔剂六次甲基四胺与微波法对表面改性的影响,评价了钒系催化剂的活性。结果表明,六次甲基四胺的添加与微波法的使用明显改善载体的表面形貌,增大载体的比表面积和平均孔径。当两者共同作用时,载体比表面积及平均孔半径分别可达72.13 m²·g^-1和9.14 nm,反应温度（350～400） ℃时,催化剂的活性最高,脱氮率最高达81.5%。     

Carbon monoxide hydrogenation over Fe/HZSM-5 catalysts. Effect of SiO2/Al2O3 zeolite ratio

Iron catalysts supported on ZSM-5 zeolites of a wide range of silica-to-alumina ratios (29-) have been prepared and tested in carbon monoxide hydrogenation. The crystalline phases of the catalysts were characterized by X-ray diffraction and their acidity by infrared spectroscopy of adsorbed pyridine. The catalytic tests were conducted at 533 K, an overall pressure of 21 bar and a feed ratio CO/H₂ close to 1. It was found that the selectivity to light olefins (C₂–C₄) increases in parallel with the increase of the Si/Al ratio of the zeolite. This was explained in terms of the decrease in Brønsted acidity of the catalysts. As a consequence, very high olefin selectivities can be achieved by decreasing the number of strong acid sites in the zeolite structure, but at the expense of high oxygenate formation.     

近单分散介孔SiO2/Fe3O4/SiO2微球的制备及漆酶固定化

以自制近单分散、平均粒径约为250 nm的SiO2亚微球为核心,采用液相沉积法得到β-FeOOH/SiO2微球,再通过溶胶-凝胶法以β-FeOOH/SiO2微球为内核,十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,经水解缩聚反应,焙烧后得到近单分散介孔SiO2/Fe3O4/SiO2微球,以复合微球为载体,对漆酶进行固定。结果表明,近单分散介孔SiO2/Fe3O4/SiO2复合微球的介孔层厚约40 nm,具有较大的饱和磁化强度(14.715 emu/g),较小的剩余矫顽力(约为109Oe),其比表面积为391.067 m2/g,孔容为0.53 cm3/g,孔径分别在5.43 nm和20～80 nm,呈现双孔径分布。复合微球吸附漆酶后,介孔材料的比表面积与孔容分别减小为103 m2/g和0.37 cm3/g,复合微球对漆酶的吸附量为202.6 mg/g。     

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

The surface environment and structural evolution of silica supported phosphotungstic acid (H₃PW₁₂O₄₀) catalysts have been investigated as a function of acid loading. H₃PW₁₂O₄₀ clusters are deposited intact upon the silica surface, adopting a Stranksi-Krastanov growth mode forming a two-dimensional adlayer which saturates at 45wt% acid. Intimate contact with the silica support perturbs the local chemical environment of three tungstate centres, which become inequivalent with those in the remaining cluster, suggesting an adsorption mode involving three terminal W==O groups. Above the monolayer, H₃PW₁₂O₄₀ clusters form three-dimensional crystallites with physico-chemical properties indistinguishable from those in the bulk heteropoly acid. These H₃PW₁₂O₄₀/SiO₂ materials are efficient for the solventless isomerisation of α-pinene under mild reaction conditions. Activity scales directly with the number of accessible perturbed tungstate sites at the silica interface; these are the active species.     

Formation of carbon nanotubes from the carbon monoxide disproportionation reaction over Co/Al2O3 and Co/SiO2 catalysts

The ammonia method has been successfully used for preparing thermostable and well dispersed alumina‐supported catalysts with a surface average size of cobalt particle D _{s= 5.7} nm. The disproportionation reaction of CO over this Co/Al₂O₃ catalyst and a similar Co/SiO₂ catalyst leads to the formation of carbon nanotubes demonstrating the same morphology. The amount of nanotubes over Co/Al₂O₃, however, is much larger than that obtained over Co/SiO₂, because of a faster ageing in the latter solid. Similar support effects have already been reported for other catalytic reactions involving carbon oxides. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ni/Al2O3-SiO2催化剂表面性质及顺酐加氢性能

以Al₂O₃质量分数为10%的Al₂O₃-SiO₂复合氧化物为载体,通过浸渍法制备一系列不同Ni负载量的Ni/Al₂O₃-SiO₂催化剂。运用BET、XRD、H₂-TPR和NH₃-TPD-MS方法研究催化剂表面性质随活性金属Ni负载量的变化规律,探讨催化剂表面性质的变化对其顺酐加氢活性、选择性及催化剂稳定性的影响。结果表明,Ni/Al₂O₃-SiO₂催化剂中的Ni质量分数由5.0%增加至12.5%时,γ-丁内酯收率由7.9%快速增至38.9%,进一步增加Ni质量分数至20.0%,γ-丁内酯收率增加趋于平缓。催化剂中Ni活性物种与催化剂酸性中心的数量是影响催化剂顺酐加氢活性的主要原因。     

AP/SiO2/Fe2O3纳米复合材料的制备与表征

采用溶胶凝胶法制备了AP/SiO2/Fe2O3纳米复合材料.用扫描电镜、X射线衍射仪(XRD)对产物的结构进行了表征.用差示扫描量热仪(DSC)对原料和产物的热分解性能进行了表征.结果表明,AP/SiO2/Fe2O3纳米复合材料是以SiO2/Fe2O3为骨架,AP进入凝胶孔洞中形成的.Fe2O3均匀分布在纳米凝胶骨架中.经热处理后αFe2O3的晶粒度为9.7nm,有效防止了纳米Fe2O3的团聚;AP均匀地分散在凝胶孔洞中,晶粒度为80～250 nm.AP/SiO2 /Fe2O3纳米复合材料能有效促进AP的热分解,使其高温分解峰温降低84.77℃,分解热提高987.1J/g.