The methanol-to-olefins (MTO) reaction is an interesting and important reaction for both fundamental research and industrial application. The Dalian Institute of Chemical Physics (DICP) has developed a MTO technology that led to the successful construction and operation of the world’s first coal to olefin plant in 2010. This historical perspective gives a brief summary on the key issues for the process development, including studies on the reaction mechanism, molecular sieve synthesis and crystallization mechanism, catalyst and its manufacturing scale-up, reactor selection and reactor scale-up, process demonstration, and commercialization. Further challenges on the fundamental research and the directions for future catalyst improvement are also suggested.

http://pubs.acs.org/doi/pdf/10.1021/acscatal.5b00007

Methanol to Olefins (MTO): From Fundamentals to Commercialization

The prediction of structure at the atomic level is one of the most fundamental challenges in condensed matter science. Here we survey the current status of the field and consider recent developments in methodology, paying particular attention to approaches for surveying energy landscapes. We illustrate the current state of the art in this field with topical applications to inorganic, especially microporous solids, and to molecular crystals; we also look at applications to nanoparticulate structures. Finally, we consider future directions and challenges in the field.

Crystal structure prediction from first principles

Probing liquid/solid interfaces at the molecular level.

Autothermal reforming of CH4 over supported Ni catalysts prepared from Mg–Al hydrotalcite-like anionic clay

Many crystalline solids cannot be prepared in the form of single crystals of sufficient size and/or quality for investigation using single-crystal X-ray diffraction techniques, and the opportunity to carry out structure determination using powder diffraction data is therefore essential to understand the structural properties of such materials. Although the refinement stage of the structure determination process can be carried out fairly routinely from powder diffraction data using the Rietveld profile refinement technique, solving crystal structures directly from powder data is associated with several intrinsic difficulties. Nevertheless, substantial progress has been made in recent years in the scope and potential of techniques in this field. This article aims to highlight the types of structural problems for which structure determination may now be tackled directly from powder diffraction data, and contemporary applications across several chemical disciplines are presented. A brief survey of the underlying methodologies is given, with some emphasis on recently developed techniques for carrying out the structure-solution stage of the structure-determination process.

Contemporary Advances in the Use of Powder X-Ray Diffraction for Structure Determination.

SAPO-34 (SAPO:  silicoaluminophosphate) has been synthesized and examined by in situ multinuclear high-resolution NMR under hydrothermal conditions (170 °C) in the presence of HF, using morpholine as the structure-directing agent. Four routes have been examined:  (a) from a SAPO gel with HF (triclinic SAPO-34), (b) from a SAPO gel without HF (trigonal SAPO-34), (c) from an AlPO4 gel with HF (triclinic AlPO4-34), and (d) from a slurry containing the layered AlPO4F prephase (triclinic AlPO4-34). In situ 13C, 19F, 27Al, and 31P NMR have uncovered the main steps of the reaction. The gel dissolves into small units condensed to no more than 4-rings (4R). The next steps are formation of a layered intermediate (the prephase), redissolution of the prephase into 4R building units of different types depending on the fluoride contents and aluminum coordination, and the subsequent nucleation and crystallization of triclinic AlPO4/SAPO-34. The initial fast process leads to the formation of the prephase made of an alter...

In Situ NMR of SAPO-34 Crystallization

The kinetics of formation of SAPO-34 in the presence of HF and with morpholine as a structure-directing agent has been monitored by in situ X-ray powder diffraction. Examination of the gel as a function of various heating profiles and final synthesis temperatures demonstrates the importance of the heating history. At lower temperatures, a layered “prephase” has been obtained with general empirical formula resembling [AlPO4F] × 0.87 C4H9ON−H. On indexing powder X-ray diffraction data, a monoclinic unit cell with dimensions a = 14.473 A, b = 6.930 A, c = 9.239 A, and β = 101.54° was found with high figures of merit. An additional disordered phase, most probably a layered structure, appears as a transient phase during transformation of the prephase to SAPO-34. It has been shown that these two precursors are of major importance for obtaining SAPO-34 under the conditions studied. In addition, use of the prephase as starting material with the addition of water produces triclinic AlPO4-34 (Si free) after hydroth...

Identification of a key precursor phase for synthesis of SAPO-34 and kinetics of formation investigated by in situ X-ray diffraction

A new aluminophosphate material UiO-7 has been prepared and the structure solved. The solution of the structure is the first known example applying the recently developed simulated annealing algorithm to identify the framework topology of an unknown structure. High-resolution synchrotron X-ray powder diffraction was then utilized to carry out a full Rietveld structure refinement. The importance of fluoride, used as a means of modifying a standard synthetic gel, is indicated by its presence as part of the structure, bridging two aluminum atoms within the cagelike building block.

UiO-7: A New Aluminophosphate Phase Solved by Simulated Annealing and High-Resolution Powder Diffraction

The stability of Mg(Al)O formed by calcination of Mg–Al-containing hydrotalcites has been studied under steam-rich conditions (H 2 O:N 2 =1:1) at 600–650 °C and 1 atm. It was found that the MgO structure as well as a high specific surface area are maintained after calcination at temperatures up to 800 °C. It has further been observed that the steam stability of Mg(Al)O towards sintering is improved after calcination of hydrotalcite at higher temperatures: calcination at 800 °C gave an improved stability of Mg(Al)O compared to calcination at 700 °C. Further, the stability towards sintering was influenced by the Mg/Al ratio of the hydrotalcite. Mg(Al)O materials formed from hydrotalcites with a Mg/Al ratio of 5 exhibit better long-term stabilisation characteristics compared to a Mg/Al ratio of 3 after calcination at 800 °C. A partial or full substitution of aluminum with gallium in the oxide did not improve the steam stability. Changing the hydrotalcite synthesis procedure from co-precipitation to the alkoxide route did not significantly alter the steam stability after calcination.

On the stability of mixed M2+/M3+ oxides

Gels prepared for the synthesis of SAPO-34, with morpholine as a structure-directing agent, have been characterized by multinuclear (1H, 13C, 19F, 27Al, and 31P), high-resolution NMR at room temperature. Less complex solutions are prepared and analyzed to aid in the peak assignment. Although some spectral features remain unresolved, the overall analysis is qualitatively consistent with the expected complex chemistry taking place in these solutions. Systems in the presence and absence of HF reveal significant spectral differences. It has been shown that pH can be monitored by the proton and carbon chemical shift of morpholine. In addition, 1H and 13C NMR spectra suggest that the structure-directing agent is an inactive species at room temperature independent of the presence or absence of HF. This is contrary to the 27Al NMR, where it has been concluded that morpholine has a significant influence on the aluminum coordination, giving tetrahedral Al when HF is absent. The existence of octahedral aluminophosph...

Duncan Akporiaye

Papers

In Situ NMR of SAPO-34 Crystallization

Identification of a key precursor phase for synthesis of SAPO-34 and kinetics of formation investigated by in situ X-ray diffraction

UiO-7: A New Aluminophosphate Phase Solved by Simulated Annealing and High-Resolution Powder Diffraction

On the stability of mixed M2+/M3+ oxides

Multinuclear NMR Analysis of SAPO-34 Gels in the Presence and Absence of HF: The Initial Gel