Hydrogen production from steam reforming of methanol over CuO/ZnO/Al2O3 catalysts: Catalytic performance and kinetic modeling

A series of CuO/ZnO/Al_2O_3, CuO/ZnO/ZrO_2/Al_2O_3 and CuO/ZnO/CeO_2/Al_2O_3 catalysts were prepared by coprecipitation and characterized by N_2 adsorption, XRD, TPR, N_2O titration and HRTEM. The catalytic performances of these catalysts for the steam reforming of methanol were evaluated in a laboratory-scale fixed-bed reactor at 0.1 MPa and temperatures between 473 and 543 K. The results showed that the catalytic activity depended greatly on the catalyst reducibility and the specific surface area of Cu. An approximate linear correlation between the catalytic activity and the Cu surface area was found for all catalysts investigated in this study.Compared to CuO/ZnO/Al_2O_3, the ZrO_2-doped CuO/ZnO/Al_2O_3 exhibited higher activity and selectivity to CO,while the CeO_2-doped catalyst displayed lower activity and selectivity. Finally, an intrinsic kinetic study was carried out over a screened CuO/ZnO/CeO_2/Al_2O_3 catalyst in the absence of internal and external mass transfer effects. A good agreement was observed between the model-derived effluent concentrations of CO(CO_2) and the experimental data. The activation energies for the reactions of methanol-steam reforming, water-gas shift and methanol decomposition over CuO/ZnO/CeO_2/Al_2O_3 were 93.1, 85.1 and 116.5 k J·mol~(-1), respectively.     

Effect of preparation methods on the hydrocracking performance of NiMo/Al2O3 catalysts

In this work, NiMo catalysts with various contents of MoO_3 were prepared through incipient wetness impregnation by a two-step method(NM-x A) and one-pot method(NM-xB). The catalysts were then characterized by XRD, XPS, NH_3-TPD, H_2-TPR, HR-TEM, and N2 adsorption–desorption technologies.The performance of the NiMo/Al_2O_3 catalysts was investigated by hydrocracking low-temperature coal tar. When the MoO_3 content was 15 wt%, the interaction between Ni species and Al_2O_3 on the NM-15 B catalyst was stronger than that on the NM-15 A catalyst, resulting in the poor performance of the former.When the MoO_3 content was 20 wt%, MoO_3 agglomerated on the surface of the NM-20 A catalyst, leading to decreased number of active sites and specific surface area and reduced catalytic performance. The increase in the number of MoS_2 stack layers strengthened the interaction between Ni and Mo species of the NM-20 B catalyst and consequently improved its catalytic performance. When the MoO_3 content reached 25 wt%, the active metals agglomerated on the surface of the NiMo catalysts, thereby directly decreasing the number of active sites. In conclusion, the two-step method is suitable for preparing catalysts with large pore diameter and low MoO_3 content loading, and the one-pot method is more appropriate for preparing catalysts with large specific surface area and high MoO_3 content. Moreover, the NMx A catalysts had larger average pore diameter than the NM-xB catalysts and exhibited improved desulfurization performance.     

Tuning the crystallite size of monoclinic ZrO_2 to reveal critical roles of surface defects on m–ZrO_2 catalyst for direct synthesis of isobutene from syngas

The effects of crystallite size on the physicochemical properties and surface defects of pure monoclinic ZrO_2 catalysts for isobutene synthesis were studied. We prepared a series of monoclinic ZrO_2 catalysts with different crystallite size by changing calcination temperature and evaluated their catalytic performance for isobutene synthesis from syngas. ZrO_2 with small crystalline size showed higher CO conversion and isobutene selectivity, while samples with large crystalline size preferred to form dimethyl ether(DME) instead of hydrocarbons, much less to isobutene. Oxygen defects(ODefects) analyzed by X-ray photoelectron spectroscopy(XPS) provided evidence that more ODefectsoccupied on the surface of ZrO_2 catalysts with smaller crystalline size. Electron paramagnetic resonance(EPR) and ultraviolet–visible diffuse reflectance(UV–vis DRS) confirmed the presence of high concentration of surface defects and Zr~(3+) on mZrO_2-5.9 sample, respectively. In situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS) analysis indicated that the adsorption strength of formed formate species on catalyst reduced as the crystalline size decreased. These results suggested that surface defects were responsible for CO activation and further influenced the adsorption strength of surface species, and thus the products distribution changed. This study provides an in-depth insight for active sites regulation of ZrO_2 catalyst in CO hydrogenation reaction.     

Effect of boron addition on the MoO_3/CeO_2–Al_2O_3 catalyst in the sulfur-resistant methanation

The effect of boron on the performance of MoO_3/CeO_2–Al_2O_3 catalysts, which were prepared with impregnation method, was investigated. The catalysts were characterized with N_2 adsorption–desorption, XRD, H_2-TPR, and NH_3-TPD, and were tested in sulfur-resistant methanation. The results indicated that the MoO_3/CeO_2–Al_2O_3 catalysts modified by boron showed higher catalytic performance in sulfur-resistant methanation. The CO conversion increased from 47% to 62% with 0.5 wt% boron content. When the content of boron was under 0.5 wt%, the results suggested there was an increase in the amorphous form of MoO_3 caused by the generation of weak and intermediate acid sites, which had weakened the interaction between the active components and supports. While, the catalyst added 2.0 wt% boron showed the strong acid sites and the largest crystalline size resulting in the uneven distribution of ceria.     

n-Decane hydro-conversion over bi- and tri-metallic Al-HMS catalyst in a mini-reactor

Bi-metallic(Pt–Sn and Sn–Ni) and tri-metallic(Pt–Sn–Ni) catalysts,supported on Al-containing hexagonal mesoporous silica(Al-HMS)(Si/Al = 20) materials,were synthesized.N_2 adsorption–desorption,X-ray diffraction(XRD),Brunauer–Emmett–Teller(BET) test,and temperature programed desorption(NH3-TPD)were used to characterize physicochemical characteristics and textural properties of the Al-HMS catalysts.Catalytic performances on hydro-cracking of n-decane at different reaction conditions were studied in a microreactor.Comparison between Pt–Sn,Sn–Ni and Pt–Sn–Ni catalyst under different hydro-cracking conditions was made.The experimental results indicate that the proper balance between the acid and metal functions is the key in synthesizing a catalyst with a better performance in hydro-cracking.Tri-metallic catalyst exhibits the best catalytic performance in n-decane hydro-cracking than two bi-metallic catalysts.     

载体对镍催化剂催化间二硝基苯加氢制间苯二胺反应性能的影响

The hydrogenation of m-dinitrobenzene to m-phenylenediamine in liquid phase was studied with the nickel catalysts supported on SiO2, TiO2, γ-Al2O3, MgO and diatomite carders. Based on the experiments of X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, temperature-programmed reduction （TPR）, temperature-programmed desorption of hydrogen （H2-TPD） and activity evaluation, the physico-chemical and catalytic properties of the catalysts were investigated. Among the catalysts tested, the SiO2 supported nickel catalyst showed the highest activity and selectivity towards m-phenylenediamine, over which 97.3% m-dinitrobenzene conversion and 95.1% m-phenylenediamine yield were obtained at 373K under hydrogen pressure of 2.6MPa after reaction for 6 h when using ethanol as solvent. Although TiO2 and diatomite supported nickel catalysts also presented high activity, they had lower selectivity towards m-phenylenediamine. As for γ-Al2O3 and MgO supported catalysts were almost inactive for the object reaction. It was shown that both the activity and selectivity of the catalysts were strongly depended on the interaction between nickel and the support. The higher activities of Ni/SiO2, Ni/TiO2 and Ni/diatomite could be attributed to the weaker metal-support interaction, on which Ni species presented as crystallized Ni metal particles. On the other hand, there existed strong metal-support interaction in Ni/MgO and Ni γ-Al2O3, which causes these catalysts more difficult to be reduced and the availability of Ni active sites decreased, resulting in their low catalytic activity.     

Rare earth metals modified Ni-S2O82-/ZrO2-Al2O3 catalysts for n-pentane isomerization

The effects of adding rare earth(RE) metals,such as Ce,Yb and Pr to Ni-S_2O_8~(2-)/ZrO_2-Al_2O_3(Ni-SZA) on the structure of catalysts as well as their isomerization performance were studied.The prepared catalysts were characterized by XRD,BET,FT-IR,Py-IR,and H_2-TPR,The results showed that the addition of RE metals can increase the strength and amounts of the acid sites,improve the redox properties of catalysts.The Yb-Ni-SZA catalyst showed the best redox properties,which could provide enough metallic sites.In addition,it provided the largest amounts of weak and moderately strong acid sites.Among RE metals modified Ni-SZA catalyst,Yb-Ni-SZA exhibited the highest isopentane yield of 61.7%at 160 °C.The optimum isomerization catalytic performance of the catalysts decreased in the order of Yb-Ni-SZA Pr-Ni-SZA Ni-SZA Ce-Ni-SZA.     

Oxygen and nitrogen-doped metal-free carbon catalysts for hydrochlorination of acetylene

Activated carbon was tested as metal-free catalyst for hydrochlorination of acetylene in order to circumvent the problem of environment pollution caused by mercury and high cost by noble metals. Oxygen-doped and nitrogen-doped activated carbons were prepared and characterized by XPS, TPD and N2 physisorption methods.The influences of the surface functional groups on the catalytic performance were discussed base on these results.Among all the samples tested, a nitrogen-doped sample, AC-n-U500, exhibited the best performance, the acetylene conversion being 92% and vinyl chloride selectivity above 99% at 240 °C and C2H2 hourly space velocity30 h-1. Moreover, the AC-n-U500 catalyst exhibited a stable performance during a 200 h test with a conversion of acetylene higher than 76% at 210 °C at a C2H2 hourly space velocity 50 h-1. In contrary, oxygen-doped catalyst had lower catalytic activities. A linear relationship between the amount of pyrrolic-N and quaternary-N species and the catalytic activity was observed, indicating that these nitrogen-doped species might be the active sites and the key in tuning the catalytic performance. It is also found that the introduction of nitrogen species into the sample could significantly increase the adsorption amount of acetylene. The deactivation of nitrogendoped activated carbon might be caused by the decrease of the accessibility to or the total amount of active sites.     

Catalytic oxidation of low concentration formaldehyde over Pt/TiO2 catalyst

Formaldehyde(HCHO) is an important indoor pollutant.Catalytic oxidize low concentration HCHO is an effective way to eliminate indoor pollution.In this study,a series of Pt/TiO_2 catalysts are prepared by impregnation and reduced by NaBH_4.The effects of loading amount of Pt and cry stal type of TiO_2 on the physical and chemical properties and the catalytic performance in HCHO oxidation reaction are investigated.The results show that the quantity of active site and the oxygen vacancy of catalysts increa sed with increasing Pt content,which is beneficial to promote the further performance of catalysts.Nevertheless,with the further rises of Pt content,the specific surface area further decreases,and the proportion of Pt~(2+) species on the catalyst surface which is significant to catalytic properties also decreases,causing catalytic performance decreases.Compared with the catalyst supporting on rutile,the Pt/α-TiO_2 catalyst supporting on anatase has larger specific surface area,more Pt~(2+) phase and easier to form oxygen vacancy in the support,which cause better catalytic performance.The catalyst with Pt content of0.1 wt% and supported by anatase TiO_2 has the best catalytic performance.The HCHO conversion efficiency reaches 98% and 100% at 50℃ and 100 ℃, and the stabilization time is longer than 140 h.     

Effect of preparation methods on the structure and catalytic performance of Fe–Zn/K catalysts for CO_2 hydrogenation to light olefins

Potassium promoted iron–zinc catalysts prepared by co-precipitation method(C–Fe–Zn/K),solvothermal method(S–Fe–Zn/K)and hydrothermal method(H–Fe–Zn/K)could selectively convert CO_2to light olefins,respectively.The physicochemical properties of the obtained catalysts were determined by SEM,N_2physisorption,XRD,H_2-TPR,CO_2-TPD and XPS measurements.The results demonstrated that preparation methods had great influences on the morphology,phase structures,reduction and adsorption behavior,and hence the catalytic performance of the catalysts.The samples prepared by hydrothermal and co-precipitation method generated small uniform particles and led to lower specific surface area.In contrast,microspheres with larger specific surface area were formed by self-assembly of nanosheets using solvothermal method.ZnFe_2O_4was the only detectable phase in the fresh C–2Fe–1Zn/K,S–3Fe–1Zn/K and S–2Fe–1Zn/K samples.ZnFe_2O_4and ZnO co-existed with increasing Zncontent in S–1Fe–1Zn/K sample,while ZnO and Fe_2O_3could be observed over H–2Fe–1Zn/K sample.All the used samples contained Fe_3O_4,ZnO and Fe_5C_2.The peak intensity of ZnO was strong in the AR-H–2Fe–1Zn/K sample while it was the lowest in the AR-C–2Fe–1Zn/K sample after reaction.The formation of ZnFe_2O_4increased the interaction between iron and zinc for C–2Fe–1Zn/K and S–Fe–Zn/K samples,causing easier reduction of Fe_2O_3to Fe_3O_4.The surface basicity of the sample prepared by co-precipitation method was much more than that of the other two methods.During CO_2hydrogenation,all the catalysts showed good activity and olefin selectivity.The CO selectivity was increased with increasing Zncontent over S–Fe–Zn/K samples.H–2Fe–1Zn/K catalyst preferred to the production of C_5~+hydrocarbons.CO_2conversion of 54.76%and C_2~=–C_4~=contents of 57.38%were obtained on C–2Fe–1Zn/K sample,respectively.     

Pt/WO3-TiO2/ZrO2-Al2O3甘油加氢体系中Al2O3的双功能催化作用研究

考察了WO3-TiO2/ZrO2-Al2O3四元氧化物中ZrO2:Al2O3质量比对Pt-WO3体系对质量分数30%甘油水溶液氢解制备1,3-丙二醇催化性能的影响，揭示了Al2O3组分在四元氧化物体系中的双功能作用。N2物理吸附脱附(BET)、X射线衍射(XRD)、傅里叶变换CO吸附及吡啶吸附红外光谱(FT-IR)、透射电镜(TEM)、程序升温还原(H2-TPR)等表征结果表明，氧化铝的掺入量直接影响到制备过程中WOx、ZrO2、TiO2等氧化物的晶相结构，进而影响到负载Pt纳米与载体的相互作用。在固定床反应器中，Pt-WO3-TiO2/ZrO2-Al2O3催化剂(Pt质量分数2%)上甘油转化率随着Al2O3质量比的升高逐渐降低，当ZrO2/Al2O3质量比为9:1时，催化活性最高，甘油转化率为38%，1,3-PDO选择性为49%，催化剂可稳定运行不低于100小时。     

α-蒎烯催化加氢催化剂制备及催化性能

采用溶胶-凝胶法制备了Al_2O_3、ZrO_2和ZrO_2/Al_2O_3载体,采用浸渍法制备了NiO/Al_2O_3、NiO/ZrO_2和NiO/ZrO_2/Al_2O_3催化剂,采用H_2-TPR、NH_3-TPD和原位红外等技术对催化剂的还原性能、表面酸特性、α-蒎烯的吸附性及比表面积等进行了表征。结果表明,负载型ZrO_2/Al_2O_3复合载体与活性物种形成较强的相互作用,稳定活性中心,复合载体Ni催化剂表面酸强度介于Ni/ZrO_2和Ni/Al_2O_3之间,α-蒎烯能与Ni/ZrO_2/Al_2O_3催化剂形成适宜化学吸附态。在α-蒎烯加氢反应中,Ni/ZrO_2/Al_2O_3催化剂表现出较好的催化活性和选择性,α-蒎烯转化率为84%,蒎烷选择性为83%。     

机械研磨燃烧法制备Cu/ZnO/Al2O3甲醇合成催化剂

引言Cu/ZnO/Al2O3催化剂近年来广泛应用于低压甲醇合成、二甲醚合成和水煤气变换等领域[1-2],该催化体系具有活性高、使用寿命长、反应温度及     

1,2-环己二醇脱氢镍基催化剂制备方法

以硝酸镍为镍源,分别以NH3.H2O,NH4HCO3,NH3.H2O+NH4HCO3为沉淀剂采用沉淀法制备镍/硅藻土催化剂,用于1,2-环己二醇脱氢制备邻苯二酚,考察了不同沉淀剂、焙烧温度、沉淀温度制备的催化剂对1,2-环己二醇脱氢反应性能的影响,并通过XRD,BET,CO2-TPD(热设计功耗)等方法对催化剂进行了表征。结果表明:不同的沉淀剂对镍的分散度、孔结构及表面碱量都有影响,以NH3.H2O+NH4HCO3复合沉淀剂制备的镍/硅藻土催化剂上活性组分镍晶粒度小、分散度较高,催化剂平均孔径较大,催化剂表面碱中心数目多、碱量大,表现出良好的催化活性和邻苯二酚选择性。另外,催化剂适宜沉淀温度为90℃、焙烧温度为350℃。上述适宜条件制备的催化剂在320℃下用于1,2-环己二醇脱氢制备邻苯二酚,1,2-环己二醇转化率达到99.1%,邻苯二酚选择性达到86.8%。     

活性形貌对CuO/ZnO/Al2O3催化加氢反应的影响

以硝酸铜、硝酸锌等为原料,采用沉淀-沉积法制备了载体是介孔Al_2O_3的CuO/ZnO/Al_2O_3催化剂,通过改变焙烧时间可得到不同活性组分形貌(团簇球状和棒状)的催化剂,并用于CO/CO_2加氢反应。通过XRD、BET、N_2吸附-脱附、TEM、H_2-TPR、CO_2-TPD、NH_3-TPD和FTIR对催化剂进行了表征与测试。结果表明,活性组分(CuO/ZnO)形貌的改变影响了催化剂的Cu O晶粒尺寸、比表面积、孔径及其还原性能,且对催化剂的酸性位点和碱性位点的相对数量影响较大。团簇球状催化剂中活性组分的分散度高、易还原、碱性位多、酸性位少,有利于甲醇的生成;而棒状催化剂中孔道不均匀、碱性位少、酸性位多,更有利于二甲醚(DME)的生成。活性测试结果表明,团簇球状催化剂表现出高甲醇选择性(95.05%)和低DME选择性(4.18%);棒状催化剂的产物选择性与团簇球状相反,表现出高DME选择性(75.41%)和低甲醇选择性(12.81%)。     

ZtO2晶相形式对Ni-B/ZrO2催化剂CO选择性甲烷化性能的影响

Amorphous Ni-B/ZrO2 catalysts were prepared by coprecipitation-chemical reduction with KBH4 aqueous solution,and various crystalline phase ZrO2(amorphous-ZrO2,tetragonal-ZrO2 and monoclinic-ZrO2) supported Ni-B catalysts were obtained by thermal treatment in 5%H2-N2 stream at different temperature.The effect of ZrO2 polymorphs and the treatment temperature on the catalytic performance for the CO selective methanation were investigated,and the catalysts were characterized by N2 physisorption,Powder X-ray diffraction(XRD), Temperature-Programmed Desorption(CO-TPD and H2-TPD),and Differential Scanning Calorimeter(DSC).The treatment temperature affected strongly the crystalline structure of ZrO2,and the CO methanation activity and selectivity of the Ni-B/ZrO2 catalysts were significantly influenced by the crystalline phase of ZrO2.Of the three forms of ZrO2 polymorphs(amorphou-ZrO2,tetragonal-ZrO2 and monoclinic-ZrO2),the amorphous-ZrO2 supported nickle catalyst showed highest CO methanation activity,attributing in large part to the largest specific surface area and the optimum CO/H2 absorption intensity of the Ni-B/amorphous-ZrO2 catalyst.     

Catalytic methanation of syngas over Ni-based catalysts with different supports

Co-precipitation method was selected for the preparation of Ni/Al2O3, Ni/ZrO2 and Ni/CeO2 catalysts, and their performances in methanation were investigated in this study. The structure and surface properties of these catalysts were characterized by BET, XRD, H2-TPD, TEM and H2-TPR. The results showed that the catalytic activity at low temperature followed the order:Ni/Al2O3>Ni/ZrO2>Ni/CeO2. Ni/Al2O3 catalyst presented the best catalytic performance with the highest CH4 selectivity of 94.5%. The characterization results indicated that the dispersion of the active component Ni was the main factor affecting the catalytic activity and the one with higher dispersion gave better performance.     

Ni-Co/Al_2O_3催化乙醇水蒸气重整制氢性能研究

利用浸渍法制备Ni-Co/Al2O3催化剂,考察催化剂组成、反应温度、水醇比、液体空速对乙醇水蒸气重整反应的影响。结果表明,Ni-Co/Al2O3催化剂中Co含量的增加会提高氢气和一氧化碳的选择性,降低甲烷和二氧化碳的选择性,催化剂Ni7.5Co7.5催化性能最佳,450℃时乙醇转化率达到100%,氢气选择性为79.78%,二氧化碳选择性为91.89%。反应温度会影响乙醇水蒸气重整制氢反应中相关反应的权重和产物的分布。加大水醇比降低一氧化碳选择性,提高二氧化碳选择性;提高液体空速,加大一氧化碳选择性。Ni-Co/Al2O3催化剂反应前后发生明显的物相重构,Co3O4被还原成Co,Co与Ni共同起活性作用,Co3O4作为催化剂前体在乙醇水蒸气重整中显示出良好的活性。     

负载型NiB非晶态合金上α-蒎烯加氢催化性能研究

采用化学还原法制备了负载型NiB非晶态合金催化剂,并运用XRD、DSC、原位红外、BET和TPD对催化剂的晶相结构、热稳定性、吸附α-蒎烯情况、表面积及表面酸特性等进行了表征,同时以α-蒎烯加氢为探针反应,考察了催化剂的活性和选择性.结果表明,α-蒎烯在NiB非晶态合金和载体的表面酸中心协同作用下形成化学吸附态,催化剂表面的酸中心强度影响催化剂的选择性,NiB/ZrO2-Al2O3催化剂使α-蒎烯的转化率达到89.6%,蒎烷选择性达到91.2%.在反应70 h后,α-蒎烯的转化率下降了近10%,而蒎烷选择性几乎保持不变.     

Influence of dehydrating agents on the oxidative carbonylation of methanol for dimethyl carbonate synthesis over a Cu/Y-zeolite catalyst

The influence of the dehydration by metal oxides on the synthesis of dimethyl carbonate(DMC) via oxidative carbonylation of methanol was studied. A Cu/Y-zeolite catalyst was prepared by the ion exchange method from CuCl_2·2 H_2O and the commercial NH_4-form of the Y type zeolite. The catalyst was characterized by X-ray fluorescence(XRF), N_2 adsorption(BET method), X-ray diffraction(XRD), and temperature-programmed desorption of ammonia(NH_3-TPD) to evaluate its Cu and Cl content, surface area, structure, and acidity. Reaction tests were carried out using an autoclave(batch reactor) for 18 h at 403 K and 5.5 MPa(2CH_3OH + 1/2O_2+CO?(CH_3O)_2CO + H_2O). The influence of various dehydrating agents(ZnO, MgO, and CaO) was examined with the aim of increasing the methanol conversion(X_(MeOH), MeOH conversion). The MeOH conversion increased upon addition of metal oxides in the order CaO MgO ZnO, with the DMC selectivity(SDMC) following the order MgO CaO ZnO. The catalysts and dehydrating agents were characterized before and after the oxidative carbonylation of methanol by thermogravimetric and differential thermogravimetric(TG/DTG), and XRD to confirm that the dehydration reaction occurred via the metal oxide(MO + H_2O → M(OH)_2). The MeOH conversion increased from 8.7% to 14.6% and DMC selectivity increased from 39.0% to 53.1%, when using the dehydrating agent CaO.