Dispersion and reactivity of Mo/Nb2O5 catalysts in the ammoxidation of toluene to benzonitrile

Abstract

A series of Mo/Nb 2 O 5 catalysts were prepared with Mo loadings ranging from 2.5-15 wt% of Mo and characterized by X-ray diffraction (XRD), pulse oxygen chemisorption, temperature-programmed desoprtion of ammonia. Dispersion of molybdena was determined by oxygen chemisorption at 623 K in a dynamic method. At low Mo loadings molybdenum oxide is found to be present in a highly dispersed state. XRD results show the presence of crystalline MoO 3 at higher Mo loadings (from 10 wt%). The dispersion of molybdena was found to decrease with increased Mo loading due to formation of MoO 3 . The catalytic properties were evaluated for the vapour phase ammoxidation of toluene to benzonitrile and are related to different characterization results.

Unprecedented Catalysis of Cs+ Single Sites Confined in Y Zeolite Pores for Selective Csp3–H Bond Ammoxidation: Transformation of Inactive Cs+ Ions with a Noble Gas Electronic Structure to Active Cs+ Single Sites

“…Here, we report the first example of the catalytic selective activation of C sp3 –H bonds to produce C–N bonds on Cs + single ion sites in Y zeolite pores (Cs + /Y) due to transformation of inactive Cs + ions with a noble gas electronic structure to active Cs + sites with HOMO­(O 2p)–LUMO­(Cs 6s) by chemical confinement of Cs + ions at Y zeolite pore surfaces, making Cs–O bonds and reactive coordination. Ammoxidation of methyl C sp3 –H bonds of aromatics with O 2 + NH 3 is an avenue for the synthesis of organic nitriles, which have been commercially used as common building blocks for high-performance rubbers, polymers, and molecular electronics and also as integral parts for producing pharmaceuticals, agrochemicals, and fine chemicals, such as vitamins, heterocycles, and various carboxylic acid derivatives. , Generally, organic nitriles were synthesized by cyanation of aldehydes using toxic hydrogen cyanide and metal cyanides, which caused environmental disasters. ,− Industrially, the vapor-phase ammoxidation of toluene to benzonitrile has been extensively studied with metal and metal oxide catalysts of V, Cr, Mo, etc., − whose catalysts possess moderate redox potentials and sufficient M–O bond strengths to provide active lattice oxygen and oxygen atoms at the catalyst surfaces for the redox catalysis. The Cs + /Y catalyst without a beneficial redox property showed a high benzonitrile yield (92.7% yield; 94.6% conversion and 98.0% selectivity at 623 K) and a high NH 3 utilization efficiency (almost no extra consumption) in toluene ammoxidation employed as a test reaction; to the best of our knowledge, this is the highest yield without NH 3 loss for the benzonitrile synthesis from toluene with O 2 + NH 3 in a single-step gas-phase reaction.…”

Structure and Reactivity of Molybdenum Oxide Catalysts Supported on La2O3-Stabilized Tetragonal ZrO2

“…Table shows the activity of various supported molybdenum oxides in comparison to the present results. The results presented in Table are from our laboratory, and more details about preparation and reactivity are found elsewhere. , The conversion of toluene is found to be more in the case of the MoO 3 /La 2 O 3 −ZrO 2 catalyst compared to those of the TiO 2 - and Nb 2 O 5 -supported catalysts, and the selectivity is more in the case of the MoO 3 /TiO 2 catalyst.…”

Vanadium–phosphorous oxide supported on mesoporous SBA-15 catalysts for ammoxidation of toluene to benzonitrile

“…Chary et al studied various supported molybdenum oxide catalysts for the toluene ammoxidation reaction and achieved a maximum of 65% toluene conversion with 71% selectivity for benzonitrile. 32 Rombia et al studied different mixed oxide catalysts for the ammoxidation of toluene and the mixed oxide catalysts of FeSiSbCrV yielded maximum toluene conversion of 35% with 45% benzonitrile selectivity. 33 Chinthala Praveen Kumar et al achieved maximum 85% conversion with 90% benzonitrile selectivity over a 5% V 2 O 5 /TiO 2 –Nb 2 O 5 catalyst.…”