Nb-Doped Vanadium Phosphorus Oxide Catalyst for the Aldol Condensation of Acetic Acid with Formaldehyde to Acrylic Acid

Abstract

Nb-doped vanadium phosphorus oxide catalysts were prepared and characterized using a variety of methods, including XRD, FT-IR, XPS, TPD and BET. The catalysts were examined for their ability to promote the aldol condensation of acetic acid with formaldehyde to acrylic acid. Catalyst composition and the conditions used to prepare the catalysts were investigated for their effects on catalytic activity. The addition of Nb changes the properties and catalytic properties of the catalyst to some extent, especially the surface acidity of catalyst and the average valence of surface V atoms, which have the greatest influence on the catalyst. When Nb/V = 0.06, the catalyst surface has the greatest acidity, the valence of surface V atoms is the lowest, and the selectivity (83.4%) and yield of acrylic acid (18.1%) are maximized.

Sustainable Acrylic Acid Making via Acetic Acid–Formaldehyde Condensation: The Highly Selective and Durable VPO-TiO2 Catalyst Accomplished by VPO Phase Control and Wet Co-Mechanical Milling

“…As versatile resin monomers, acrylic acid (AA) and methyl acrylate (MA) are widely employed for the production of biomimetic materials, PAN fibers, adhesives, plastics, and hydrogels, etc. − Currently, the major route of AA (MA) production is a successive two-step oxidation of propylene. − However, this traditional route is thought to be nonsustainable and closely dependent on the petrochemical resources, due to the petroleum-based propylene feedstock . Hence, the motivation to explore a replaceable route for acrylic acid (methyl acrylate) through sustainable resources has garnered increased attention. − Recently, a new AA (MA) product route based on the condensation reaction between acetic acid (HAc) and formaldehyde (FA) has attracted broad attention by both academic and industrial communities, due to its technical ease and the advantage that the feedstock (both HAc and FA) could be produced from biomass, natural gas, and coal, and is becoming less expensive. ,,,, …”

“…12−14 Recently, a new AA (MA) product route based on the condensation reaction between acetic acid (HAc) and formaldehyde (FA) has attracted broad attention by both academic and industrial communities, due to its technical ease and the advantage that the feedstock (both HAc and FA) could be produced from biomass, natural gas, and coal, and is becoming less expensive. 3,5,11,15,16 In reality, the gas phase condensation between HAc and FA is an acid−base catalyzed reaction, 16−18 and the key to accomplishing this route is to develop a highly efficient and durable solid acid or base catalyst, or an acid−base bifunctional catalyst, which should be highly selective to the target products, with a reasonable level of conversion, and particularly, an improved catalyst durability. In the early days, Vitcha and Sims 19 proposed a base-catalyzed mechanism for the HAc-FA condensation, namely, HAc first adsorbs on the basic catalyst surface to form a carbanion, followed by C− C bond formation, proton transfer, and dehydration to produce target products.…”

“…Li and co-workers 23 prepared a series of metal cation-doped VPO catalysts and found that a VPO catalyst doped with 2% Zr showed the highest activity. Zhu and co-workers 3 reported that the Nb doping could modify the catalyst surface acidic property and the oxidation state of V atoms, and enhance the catalyst activity accordingly.…”

High-efficiency and durable V–Ti–Nb ternary catalyst prepared by a wet-solid mechanochemical method for sustainably producing acrylic acid via acetic acid–formaldehyde condensation

“…Undoubtedly, the medium acid site density of the catalyst VTi–Nb was slightly higher than that of the catalyst VTi–Mo and considerably greater than that of the catalysts VTi–W and VTi–Bi. However, in theory, the order of the medium acid site density on the VPO surface should be similar to the order of the V 5+ /V 4+ ratios (Table 1), because the literature 13,22,25 show that the surface V 5+ specimen is the main factor determing the medium acid site density. The situation was caused by the differential metal cation exposure density.…”

“…For the past few years, a new procedure to prepare AA (MA) by aldol condensation between acetic acid (HAc) and formaldehyde (HCHO) has been widely studied by academia and industry, [12][13][14][15][16][17][18][19][20] because raw materials such as HAc and HCHO can be obtained from sustainable biomass or low-cost natural gas, and coal. In fact, the aldol condensation reaction between HAc and HCHO conforms to an acid-base catalytic mechanism, 21,22 and multifarious types of acid-base catalysts such as alkali metals supported on silica-based materials, 23 ionic liquids, 24 acidic zeolites, 14 and vanadium phosphorus oxide (VPO) 25 have been developed and applied to the target condensation reaction.…”