Anthony F. Volpe

Structural aspects of the M1 and M2 phases in MoVNbTeO propane ammoxidation catalysts

Abstract The structures of M1 and M2 in MoVNbTeO propane ammoxidation catalysts have been solved using a combination of TEM, neutron powder diffraction, and synchrotron X-ray powder diffraction. The unit cell of M1 is Pba2 (No. 32) with a = 21.134(2) Å, b = 26.658(2) Å, c = 4.0146(3) Å and Z = 4. The formula unit is Mo7.8V1.2NbTe0.937O28.9. The unit cell of M2 is Pmm2 (No. 25) with a = 12.6294(6) Å, b = 7.29156(30) Å, c = 4.02010(7) Å and Z = 4. The formula unit is Mo4.31V1.36Te1.81Nb0.33O19.81. Tellurium sites in hexagonal channels of both phases are displaced toward vanadium-occupied framework sites, whereas Te in the heptagonal channel of M1 is near the channel center. The chemical topology resulting from oxidation states and Madelung site potentials presents active moieties for the ammoxidation of propane in M1 and propene in M2. EPR confirmed the presence of V4+ and possibly Mo5+ in M1 and V4+ in M2.

Structural Characterization of the Orthorhombic Phase M1 in MoVNbTeO Propane Ammoxidation Catalyst

The structure of the orthorhombic phase in the MoVNbTeO propane ammoxidation catalyst system has been characterized and refined using a combination of TEM, synchrotron X-ray powder diffraction (S-XPD), and neutron powder diffraction (NPD). This phase, designated as M1 by Ushikubo et al. [1], crystallizes in the orthorhombic space group Pba2 (No. 32) with a = 21.134(2) Å, b = 26.658(2) Å, and c = 4.0146(3) Å. The formula unit is Mo7.5V1.5NbTeO29. Bond valence sum calculations indicate the presence of d1 metal sites neighbored by d0 metal sites. The d1 sites are occupied by a distribution of Mo5+ and V4+, whereas the d0 sites are occupied by a distribution of Mo6+ and V5+. Out-of-center distortions in d0 octahedra are consistent with the second-order Jahn–Teller effect and lattice effects. We argue that the V5+–O–V4+/Mo5+ moieties adjacent to Te4+ and Mo6+ sites in the [001] terminal plane provide a spatially isolated active site at which the selective ammoxidation of propane occurs.

Applications of Combinatorial Methods in Catalysis

With rising economic demands for higher efficiency and productivity in research and development, combinatorial catalysis is increasingly being implemented to bring more catalysts per unit time to the marketplace. High-throughput automated synthesis and advanced screening technologies are now being applied to the discovery of more efficient homogeneous as well as heterogeneous catalysts and materials. The combinatorial process allows the exploration of large and diverse compositional and parameter spaces by establishing an integrated workflow of rapid parallel or combinatorial synthesis of large numbers of catalytic materials, subsequent high-throughput assaying of these compounds and large-scale data analysis. The number of experiments that can be screened has risen by orders of magnitude resulting in a much higher probability of discovering new catalysts or materials. The goal of this review is to provide an overview of selected advances that have been made in this rapidly growing field in both academia and industry over the past several years.

Gas phase oxidation of ethane to acetic acid using high-throughput screening in a massively parallel microfluidic reactor system

Abstract High-throughput primary synthesis and screening methods have been applied to the heterogeneously-catalyzed gas phase oxidation of ethane to acetic acid using mixed metal oxide catalysts. The discovery libraries consisted of 16×16 arrays of 256 catalysts on 3″×3″ quartz wafers. Catalysts were prepared using automated liquid-dispensing techniques and screened in parallel for catalytic activity in a Symyx Technologies 256-channel microfluidic reactor. Product detection was performed using parallel colorimetric techniques on products adsorbed on silica-coated glass TLC plates. This workflow allows the screening of more than 3000 samples per day. Promising leads were confirmed in focus libraries and are being optimized in secondary screening. MoV was identified as the most active binary of redox metals and was subsequently doped with main group, rare earth, and transition metals to form ternaries. Prior art MoVX (X=Nb, Ni, Sb) catalysts were successfully reproduced and it was shown that Pd doping significantly increases the catalytic activity of these systems. Three novel MoVY ternary systems were discovered.

High-throughput approaches to catalyst discovery.

High-throughput synthesis and screening approaches to catalyst discovery and optimization are systematically changing the way in which catalyst research is conducted. Increased rates of innovation, cost effectiveness, improved intellectual property, reduced time to market and an improved probability of success are some of the attractive features that demand consideration. Advances made over the past few years reveal that any initial skepticism is waning, and high-throughput approaches to catalyst discovery are now being implemented broadly in industrial and academic laboratories.

High throughput screening of low temperature CO oxidation catalysts using IR thermography.

The catalytic oxidation of carbon monoxide to carbon dioxide is an important process used in several areas such as respiratory protection, industrial air purification, automotive emissions control, CO clean-up of flue gases and fuel cells. Research in this area has mainly focused on the improvement of catalytic activity at low temperatures. Numerous catalyst systems have been proposed, including those based on Pt, Pd, Rh, Ru, Au, Ag, and Cu, supported on refractory or reducible carriers or dispersed in perovskites. Well known commercial catalyst formulations for room temperature CO oxidation are based on CuMn2O4 (hopcalite) and CuCoAgMnOx mixed oxides. We have applied high-throughput and combinatorial methodologies to the discovery of more efficient catalysts for low temperature CO oxidation. The screening approach was based on a hierarchy of qualitative and semi-quantitative primary screens for the discovery of hits, and quantitative secondary screens for hit confirmation, lead optimization and scale-up. Parallel IR thermography was the primary screen, allowing one wafer-formatted library of 256 catalysts to be screened in approximately 1 hour. Multi-channel fixed bed reactors equipped with imaging reflection FTIR spectroscopy or GC were used for secondary screening. Novel RuCoCe compositions were discovered and optimized for CO oxidation and the effect of doping was investigated for supported and bulk mixed oxide catalysts. Another family of active hits that compare favorably with the Pt/Al2O3 benchmark is based on RuSn, where Sn can be used as a dopant (e.g. RuSn/SiO2) and/or as a high surface area carrier (e.g., SnO2 or Sn containing mixed metal oxides). Also, RuCu binary compositions were found to be active after a reduction pretreatment with hydrogen.

High Throughput Discovery of Families of High Activity WGS Catalysts: Part I - History and Methodology

State-of-art water gas shift catalysts (FeCr for high temperature shift and CuZn for low temperature shift) are not active enough to be used in fuel processors for the production of hydrogen from hydrocarbon fuels for fuel cells. The need for drastically lower catalyst volumes has triggered a search for novel WGS catalysts that are an order of magnitude more active than current systems. Novel catalytic materials for the high, medium and low temperature water gas shift reactions have been discovered by application of combinatorial methodologies. Catalyst libraries were synthesized on 4 inch wafers in 16 x 16 arrays and screened in a high throughput scanning mass spectrometer in the temperature range 200 degrees C to 400 degrees C. More than 200 wafers were screened under various conditions and more than 250,000 experiments were conducted to comprehensively examine catalyst performance for various binary, ternary and higher-order compositions.

High-throughput materials chemistry

The speed and efficiency of research aimed at the discovery and optimization of catalysts, polymers,…