Surface Dynamics of A Vanadyl Pyrophosphate Catalyst for n‐Butane Oxidation to Maleic Anhydride: An In Situ Raman and Reactivity Study of the Effect of the P/V Atomic Ratio

Abstract

This work focused on investigating the effect of the P/V atomic ratio in vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride, on the nature of the catalytically active phase. Structural transformations occurring on the catalyst surface were investigated by means of in situ Raman spectroscopy in a non-reactive atmosphere, as well as by means of steady-state and non-steady-state reactivity tests, in response to changes in the reaction temperature. It was found that the nature of the catalyst surface is affected by the P/V atomic ratio even in the case of small changes in this parameter. With the catalyst having P/V equal to the stoichiometric value, a surface layer made of alpha(Iota)-VOPO(4) developed in the temperature interval 340-400 degrees C in the presence of air; this catalyst gave a very low selectivity to maleic anhydride in the intermediate T range (340-400 degrees C). However, at 400-440 degrees C delta-VOPO(4) overlayers formed; at these conditions, the catalyst was moderately active but selective to maleic anhydride. With the catalyst containing a slight excess of P, the ratio offering the optimal catalytic performance, delta-VOPO(4) was the prevailing species over the entire temperature range investigated (340-440 degrees C). Analogies and differences between the two samples were also confirmed by reactivity tests carried out after in situ removal and reintegration of P. These facts explain why the industrial catalyst for n-butane oxidation holds a slight excess of P; they also explain discrepancies registered in the literature about the nature of the active layer in vanadyl pyrophosphate.

Structure–Reactivity Correlations in Vanadium‐Containing Catalysts for One‐Pot Glycerol Oxidehydration to Acrylic Acid

“…Different states of Vi ons can be evidenced; both V 5 + (binding energy (BE): 517.1 eV)a nd V 4 + (BE: 516.1 eV) ions can be detected on the WV sample, whereas ah igherV 5 + /V 4 + surfacer atio is shown for the extra-framework Vs pecies in the ion-exchanged sample, VO-WO x .C onsidering that the ion exchange was performed by using vanadyl ions (VO 2 + ), the XPS results point out ap artial oxidation process during catalystp reparation, consistently more severe in the case of the extra-framework Vs pecies. Moreover,t he VPP catalystp resentsV 4 + as the predominant species, but the presence of V 5 + is also significant, despite the fact that the XRD pattern only shows the presence of (VO) 2 P 2 O 7 ;t his observation agrees with previousr eports by other authors, [35][36][37] who attribute the presence of V 5 + speciest ot he coexistence of VOPO 4 domains in additiont o( VO) 2 P 2 O 7 on the surface of the catalyst. Finally,t he VCoAPO sample shows both V 5 + /V 4 + ions, whereas V 5 + is mainly observed on the VO x /VCoAPOs ample.…”

Hydrothermal Syntheses and Crystal Structures of Two New Vanadium Phosphates

“…Though vast numbers of vanadium phosphates have been reported, most of them possess infinite structures including one-dimensional (1D) [17][18][19], two-dimensional (2D) [20][21][22][23], and threedimensional (3D) [24][25][26][27][28], whereas only a few examples are discrete [29][30][31]. In this work, we successfully synthesized two new discrete vanadium phosphates (NH 4 ) 5 . Structural analysis indicates that the solubility of the V reactants (NH 4 VO 3 for 1 and V 2 O 5 for 2) plays an important role in the formation of the vanadium phosphates.…”

“…The vanadium phosphates (VPOs), as an important family of transition-metal phosphates, have been studied intensively since vanadyl pyrophosphate (VO) 2 P 2 O 7 was reported to be a catalyst for synthesis of maleic anhydride from light hydrocarbons [1][2][3][4][5]. In the last few years, extensive interest has arisen in VPO crystal chemistry due to their rich structural diversity and potential applications in adsorption, shape-selective catalysis, ion exchange, magnetism, and nonlinear optics [6][7][8][9][10][11].…”

A New Process for Maleic Anhydride Synthesis from a Renewable Building Block: The Gas‐Phase Oxidehydration of Bio‐1‐butanol

“…Catalytic tests were carried out in aq uartz continuous-flow reactor by using an inlet feed containing 1% 1-butanol in air,w ith W/F = 1.33 gsmL À1 .P roducts were analysed online by sampling av olume of the outlet gas stream, which was injected into ag as chromatograph equipped with two columns:H P-1 for the separation of 1butanol, C 4 hydrocarbons, MA, formaldehyde, acetic acid and acrylic acid, and Carbosieve SII to analyse O 2 ,CO, and CO 2 . [88,89] DRIFT spectroscopy-mass spectrometry…”