Effect of Mo Species on the Selective Oxidation of n‐Butane to Maleic Anhydride over Mo‐Promoted VPP

Abstract

Vanadyl pyrophosphate contained catalysts (VPP) are of great importance for the selective oxidation of light alkane to chemicals. Achieving high conversion of alkane with a high selectivity of target products is critical for the practical applications of VPP. Here we selected three Mo species H5Mo12O41P (PMA), MoO3, and (NH4)6Mo7O4⋅4H2O (HAM) as promoters for VPP catalysts. Performance evaluation shows that all Mo‐promoted VPP catalysts have much better catalytic performance than those without Mo promoter, which are mainly attributed to the different Mo species could induce the formation of active crystal and affect the redox characteristic to varying degrees. Moreover, SEM revealed that the PMA possess a “shape memory” function, which result in crystallinity of (200) in PMA‐VPO is higher than others. H2‐TPR suggested that PMA could increase the amount of oxygen and reduce the reduction activation energy, which is beneficial to enhance the activity of VPP. The presented results may be helpful for selecting superior metal promoter and facilitated the process of VPP catalyst development for n‐butane selective oxidation.

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“…50,66 Meanwhile, from Table S2, we can see that the amounts of reactive oxygen of VPO−DES is higher than that for VPO-Blank, which could enhance the performance for the selective oxidation of n-butane to MA. 4,7 These results are also in keeping with the catalytic performance.…”

“…All catalysts reveal two peaks within the range of 550–730 °C (Figure S4). The first peak located at around 580 °C is associated with the reduction of V 5+ , and the second peak appears at around 700 °C, corresponding to the removal of lattice oxygen from V 4+ phase. ,, Obviously, the reduction temperature of VPO–DES-0.6 is significantly decreased compared with that for the VPO-Blank, which is beneficial to the realization of the catalytic cycle. , Meanwhile, from Table S2, we can see that the amounts of reactive oxygen of VPO–DES is higher than that for VPO-Blank, which could enhance the performance for the selective oxidation of n -butane to MA. , These results are also in keeping with the catalytic performance.…”

“…It will be relatively reduced the adsorption capacity of MA on the catalysts surface with the decrease of total acids and prohibited its over oxidation. Meanwhile, the presence of DES leads to the enrichment of P on VPO surface, correspondingly increasing MA selectivity to some extent as shown in Figure d due to the different reorganization energies of VO and PO on the catalyst surface. ,,, …”

“…From the above discussion, the total acidity on the surface is decreased with the introduction of ChCl/GLU DES, which is able to accelerate the n -butane desorption from the surface of catalysts, avoiding over oxidization of MA. In addition, the presence of DES lead to the enrichment of P on VPO surface, increasing the selectivity of MA due to the different reorganization energies of VO and PO on the catalyst surface. ,,, What is more, the crystallinity and the number of active sites are significantly increased after introducing DES, which can reduce the consumption of active intermediates and provide more reaction sites. All these contribute to the enhancement of catalytic performance.…”

“…With the development of the petroleum industry, a mass of low carbon alkanes (C1–C5) are produced as byproducts every year. Recently, the functionalization of low carbon alkanes has attracted a lot of interests not only in the laboratory, but also in industry. − Up to now, vanadium phosphorus oxide (VPO) mixed oxide is the only catalyst that achieves low carbon alkanes transformed to high-value chemicals in industry. Since the VPO catalyst was discovered, numerous studies have been carried out in order to investigate the intrinsic properties of VPO, including the physicochemical properties, preparation routes, phase transformation, active phases, catalytic mechanism, etc., and to improve further the catalytic performance. − The crystalline phase of the VPO precursor was confirmed first by Johnson et al in 1984 .…”