Comparison of MoVTaTeO and MoVNbTeO <Emphasis Type="Italic">M1</Emphasis> crystal chemistry

The structure of a new catalytically active MoVTaTeO variant of the M1-phase propane (amm)oxidation catalyst has been refined. This Ta-containing variant is isostructural with the well-known MoVNbTeO form of the M1 phase, in this case with a = 21.1484(9) ?, b = 26.6472(11) ?, c = 4.00332(1) ? with Z = 4. The formula unit of can be written as (TeO)_0.43 Mo_4.08 V_0.70Ta_0.22O₁₄ to be compared to the previously determined composition for the Nb-containing phase: (TeO)_0.47Mo_3.98V_0.59Nb_0.43O₁₄. The Ta-containing variant is somewhat vanadium-rich compared to its Nb counterpart, but the Ta solubility is only about half of the corresponding Nb solubility. Debate over the true location and role of Nb in the MoVNbTeO M1 phase may be better understood by comparison with the refined structure of this chemically similar Ta analog. In this case Ta is clearly distinguishable from each of the other metals from scattering experiments, unlike Nb.     

丙烷氨氧化制丙烯腈工艺以及催化剂研究进展

由于原料丙烯的短缺以及对丙烯腈需求的不断增加,本文提出一种以丙烷为原料的丙烯腈生产路线,并主要介绍了丙烷氨氧化反应的两种工艺和几种有发展前景的催化剂,为丙烯腈生产提供了一条具有经济吸引力的新路线。     

A Study of the Functionalities of the Phases in Mo–V–Nb–Te Oxides for Propane Ammoxidation

Catalysts belonging to the Mo–V–Nb–Te–O system have been prepared with both a slurry method and hydrothermal synthesis and were tested for propane and propylene ammoxidation to acrylonitrile. All samples were characterized with BET, XRD, ICP and XPS. The catalysts were found to consist of three phases, to which activity and selectivity correlations were made. The results indicate that both an orthorhombic phase and a hexagonal phase are needed to have an active and selective catalyst. The orthorhombic phase is the most active for propane conversion although less selective than the hexagonal phase for the conversion of formed propylene to acrylonitrile.     

Genesis of site isolation and phase cooperation in selective oxidation catalysis

Two of the important principles governing selective oxidation catalysis are site isolation and phase cooperation. They are discussed here in light of their inception, development, historic perspective and current acceptance in the field of selective oxidation and ammoxidation catalysis.     

Fundamental Principles of Selective Heterogeneous Oxidation Catalysis

Seven principles (seven pillars) underpinning selective heterogeneous oxidation catalysis, comprising lattice oxygen, metal-oxygen bond strength, host structure, redox, multifunctionality of active sites, site isolation, and phase cooperation are described. Their intended utilization towards a deeper understanding of metal oxide catalyst behavior and application towards catalyst design are indicated.     

镍基催化剂气固相催化丙烯腈加氢合成丙腈

为研究丙烯腈气固相加氢制备丙腈的催化剂,采用浸渍法制备了一种镍基催化剂,在固定床反应器中考察了Ni-Cu-Zn负载量、反应温度、反应压力、液时空速(LHSV)及氢腈物质的量比对催化剂性能的影响,并对催化剂的稳定性进行了研究。实验结果显示,使用质量组成为5.7%Ni、1.4%Cu、1.4%Zn的催化剂,当反应温度150℃、反应压力0.5 MPa、丙烯腈液时空速为0.24 h-1、氢腈物质的量比为12时,丙烯腈的转化率为96%,丙腈选择性可达94.9%。     

The importance of site isolation and phase cooperation in propane ammoxidation on rutile-type vanadia catalysts

Propane ammoxidation to acrylonitrile over rutile-type vanadia catalysts is discussed regarding phase cooperation and site isolation effects. Compared with the pure phases, biphasic catalysts with both SbVO₄and -Sb₂O₄are considerably more selective to the formation of acrylonitrile. It is demonstrated that cooperation between the phases during the calcination of the catalyst and the use in propane ammoxidation results in spreading of antimony species from free antimony oxide to the surface of SbVO₄, forming Sb⁵⁺–V³⁺/V⁴⁺supra-surface sites being involved in the formation of acrylonitrile. Dilution and isolation of the vanadium centers in SbVO₄through the partial replacement with, e.g., Al, Ti and W improves the catalytic properties. Structure–reactivity correlations using data for a nominal Sb_0.9V_0.9-x Ti _x O _y series indicate that the activation of propane occurs on a V³⁺site and the activation of ammonia requires an Sb⁵⁺site.     

2-甲氧基-4-丙烯基苯基苄基醚的相转移催化合成研究

在相转移催化剂存在下,以2-甲氧基-4-丙烯基苯酚、氯化苄为原料合成2-甲氧基-4-丙烯基苯基苄基醚,分别研究了反应温度、反应时间、原料配比、催化剂用量等条件对合成反应的影响．确定了最佳工艺条件。该方法合成2-甲氧基-4-丙烯基苯基苄基醚的最佳工艺条件是：反应温度95℃;反应时间2h;n(2-甲氧基-4-丙烯基苯酚)：n(氯化苄)=1：1,05;n(2-甲氧基-4-丙烯基苯酚)：n(氢氧化钾)=1：1．10;催化剂=5．89％(相对于2-甲氧基-4-丙烯基苯酚质量分数),2-甲氧基-4-丙烯基苯基苄基醚的收率可达到92．52％以上,产品纯度98．5％。     

Surface active sites present in the orthorhombic M1 phases: low energy ion scattering study of methanol and allyl alcohol chemisorption over Mo–V–Te–Nb–O and Mo–V–O catalysts

The outermost surface compositions and chemical nature of active surface sites present on the orthorhombic (M1) Mo–V–O and Mo–V–Te–Nb–O phases were determined employing methanol and allyl alcohol chemisorption and surface reaction in combination with low energy ion scattering (LEIS). These orthorhombic phases exhibited vastly different behavior in propane (amm)oxidation reactions and, therefore, represented highly promising model systems for the study of the surface active sites. The LEIS data for the Mo–V–Te–Nb–O catalyst indicated surface depletion for V (−23%) and Mo (−27%), and enrichments for Nb (+55%) and Te (+165%) with respect to its bulk composition. Only minor changes in the topmost surface composition were observed for this catalyst under the conditions of the LEIS experiments at 400 °C, which is a typical temperature employed in these propane transformation reactions. These findings strongly suggested that the bulk orthorhombic Mo–V–Te–Nb–O structure is terminated by a unique active and selective surface layer in propane (amm)oxidation. Moreover, direct evidence was obtained that the topmost surface VO _x sites in the orthorhombic Mo–V–Te–Nb–O catalyst were preferentially covered by chemisorbed allyloxy species, whereas methanol was a significantly less discriminating probe molecule. The surface TeO _x and NbO _x sites on the Mo–V–Te–Nb–O catalyst were unable to chemisorb these probe molecules to the same extent as the VO _x and MoO _x sites. These findings suggested that vastly different catalytic behavior exhibited by the Mo–V–O and Mo–V–Te–Nb–O phases is related to different surface locations of V⁵⁺ ions in the orthorhombic Mo–V–O and Mo–V–Te–Nb–O catalysts. Although the proposed isolated V⁵⁺ pentagonal bipyramidal sites in the orthorhombic Mo–V–O phase may be capable of converting propane to propylene with modest selectivity, the selective 8-electron transformation of propane to acrylic acid and acrylonitrile may require the presence of several surface VO _x redox sites lining the entrances to the hexagonal and heptagonal channels of the orthorhombic Mo–V–Te–Nb–O phase. Finally, the present study strongly indicated that chemical probe chemisorption combined with low energy ion scattering (LEIS) is a novel and highly promising surface characterization technique for the investigation of the active surface sites present in the bulk mixed metal oxides.