New approach on the catalytic oxidation of methanol to formaldehyde over MoO₃ supported on nano hydroxyapatite catalysts

Abstract

Molybdenum oxide (20 wt. %) supported on nano hydroxyapatite mixed was prepared by impregnation method and calcinated at 400 o , 500 o , 600 o and 700 o C in static air atmosphere. The catalysts were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and nitrogen sorption measurements. The gas-phase oxidation of methanol to formaldehyde was carried out in a conventional fixed flow bed reactor. The obtained results clearly revealed that the formation of CaMoO 4 spinel nano particles was active and selective catalyst towards the formation of formaldehyde. The maximum yield of formaldehyde was 97% on the catalyst calcined at 400 o C. Moreover, the yield of formaldehyde was found unaffected by increasing the calcination temperature up to 700 o C. Keywords: MoO 3 ; nano hydroxyapatite support; structure; surface area; oxidation; methanol. IntroductionHydroxyapatite (HAP) has attracted the attention of researchers to biomaterials field in recent years [1]. HAP is a highly non-stoichiometric calcium phosphate compound with a Ca/P molar ratio ranging from 1.5 to 1.67. Moreover, HAP also is known [2] to have the character of both acidic and a basic catalyst when its Ca/P ratio is between 1.5 and 1.67. On the other hand, formaldehyde is obtained from oxidative dehydrogenation of methanol by two commercial processes: (i) On iron-molybdate based catalysts and (ii) On silver based catalysts. In both processes, a conversion of about 99 % and 92 % selectivity respectively are obtained the temperature of reaction is about 400 o C in the first and 650 o C in the second process. The silver process has high operating costs due to steam consumption. Moreover, the selective oxidation of methanol to formaldehyde takes place on MoO 3 mixed oxide catalysts [3,4]. However, the catalytic gas oxidation of methanol to formaldehyde over MoO 3 supported on nano hydroxyapatite to our knowledge has not yet been reported. Therefore, the main objective of the present work is synthesis of formaldehyde by oxidative dehydrogenation of methanol over MoO 3 (20 wt %) supported on n-HAP as a competitive catalyst with previous applied industrial catalysts.

Thermooxidative degradation of polyoxymethylene homo- and copolymer nanocomposites with hydroxyapatite: Kinetic and thermoanalytical study

“…Synthesis of formaldehyde by oxidative dehydrogenation of methanol over MoO 3 supported on non-stoichiometric HAp as a competitive catalyst with previous applied industrial catalysts has been reported, too [39]. In the work by Matsumura and Moffat [40] it was revealed that on hydroxyapatite of stoichiometric composition (Ca/P = 1.65), methanol decomposes at 600°C, in the absence of oxygen, producing predominantly carbon monoxide.…”

Highly Stable Apatite Supported Molybdenum Oxide Catalysts for Selective Oxidation of Methanol to Formaldehyde: Structure, Activity and Stability

“…Under anaerobic conditions a 5 wt% MoO 3 /CaHAP catalyst has previously been reported to have high selectivity and stability for the dehydrogenation of methanol to formaldehyde, although at very low activity, [52,53] but to the best of our knowledge we report the first investigation with oxygen in the feed, making the catalysts relevant for industrial application in the Formox process. This paper reports part one of the investigation, part two was performed on industrial sized catalyst pellets, investigating the influence of pellet density.…”

A Review and Experimental Revisit of Alternative Catalysts for Selective Oxidation of Methanol to Formaldehyde

“…The active sites were concluded to be Mo 6+ , which produced Lewis and Brønsted acid sites of weak and intermediate strength [108]. The active phase of the catalyst was suggested to be calcium molybdate formed under calcination [108,109]. Thrane et al [110] investigated MoO 3 supported on hydroxyapatite and the Sr analogue in a feed of 150 NmL/min, 5 vol.% MeOH, and 10 vol.% O 2 in N 2 .…”