Silica-titania supported vanadia catalysts in the utilization of industrial sulfur-contaminated gaseous methanol streams

Abstract Volatile organic compounds (VOCs) are considered as one class of the major contributors to air pollution. Strict limits have been set for these emissions due to their harmful effects on human health and the environment. In addition to legislation, technology and material development during the past decades has pushed forward the development of VOC emission abatement technologies. Advancements in material research and widening the adaptation of the circular economy concept have led to the idea of utilizing harmful VOC compounds as novel raw materials to produce chemicals. In this work, the possibility of producing formaldehyde from sulfur-contaminated methanol originating from the pulp and paper industry was investigated. Silica-titania supported vanadia (VOx/SiO2+TiO2) catalysts in different compositions were selected as the focus of the study. The aim was to investigate the material activity in the oxidative dehydrogenation and oxidative desulfurization of a mixture of methanol and methyl mercaptan. In addition, several characterization methods were used to reveal the chemical and physical properties of the materials used. For example, in situ DRIFT studies were performed to discover the surface species during the production of formaldehyde from methanol. The results prove the high activity of the studied vanadia catalyst supported on silica-titania in the simultaneous conversion of methanol and methyl mercaptan to formaldehyde. The activity of the catalyst is influenced by its composition, especially the silica-titania ratio of the support. Depending on the support material, and the temperature and gas conditions during preparation, changes in the quality of the vanadia species on the support surface can be observed. The stability of polymeric vanadia species is in connection with the enhanced formaldehyde production. The optimal reaction temperature is dependent on the reducibility of the catalyst, which should be optimized since reducibility is also connected with the unwanted further oxidation of formaldehyde. The study provides new knowledge on using VOx/SiO2+TiO2 in environmental applications. The research advances the utilization of industrial gaseous VOC streams and opens new pathways toward new innovations.Tiivistelmä Haihtuvat orgaaniset yhdisteet (VOC) ovat ryhmä merkittäviä ilmansaasteita. Teollisuuden VOC-yhdisteille on asetettu lainsäädännössä tiukat rajoitukset niiden ympäristö- ja terveyshaittojen vuoksi. Päästömäärien rajoittamisen lisäksi myös VOC-yhdisteiden käsittelymenetelmiä on kehitetty eteenpäin viime vuosikymmenten aikana. Teollisuusprosessien päästöjen käsittelystä on tullut kustannustehokkaampaa edistyneiden teknologioiden ja kehittyneiden materiaalien kautta. Nykyiset kiertotaloustavoitteet ovat osaltaan johtaneet tässä työssä ideaan kaasumaisten VOC-päästöjen hyötykäytöstä. Tässä työssä tutkittiin selluteollisuudessa muodostuvan, rikkiyhdisteillä kontaminoituneen metanolin reagoimista formaldehydiksi pii- ja titaanidioksidituettujen vanadiinikatalyyttien (VOx/SiO2+TiO2) avulla. Työn pääpainona oli materiaalien aktiivisuuden selvittäminen metanoli- ja metyylimerkaptaani -seoksen reaktioissa. Tämän lisäksi käytettyjä materiaaleja karakterisoitiin eri menetelmillä. Työssä tehtiin myös in situ DRIFT-kokeita valituissa reaktio-olosuhteissa katalyyttisten pintojen toiminnan selvittämiseksi. Tulokset osoittivat, että pii- ja titaanidioksidituettu vanadiini eri oksidimuodoissaan on aktiivinen katalyyttimateriaali lähtöaineiden samanaikaisissa reaktioissa formaldehydiksi. Katalyytin koostumuksella, erityisesti tukiaineen koostumussuhteella ja valmistuksessa käytetyillä olosuhteilla on merkitystä katalyytin aktiivisuuteen. Kyseiset muuttujat vaikuttavat erityisesti vanadiinin pintayhdisteiden laatuun. Polymeerisen vanadiinioksidin läsnäolo tehostaa formaldehydin muodostumista. Reaktion optimilämpötila on kytköksissä katalyytin pelkistyvyyteen, mutta hyvä pelkistyvyys johtaa helposti myös formaldehydin edelleen reagoimiseen. Työ edistää teollisuuden päästökaasujen hyötykäytön mahdollisuuksien tunnistamista ja avaa mahdollisuuksia kohti uusia ympäristöinnovaatioita

Catalytic activity studies of vanadia/silica–titania catalysts in SVOC partial oxidation to formaldehyde:focus on the catalyst composition

Abstract In this work, silica–titania supported catalysts were prepared by a sol–gel method with various compositions. Vanadia was impregnated on SiO₂-TiO₂ with different loadings, and materials were investigated in the partial oxidation of methanol and methyl mercaptan to formaldehyde. The materials were characterized by using N₂ physisorption, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), Scanning transmission electron microscope (STEM), NH₃-TPD, and Raman techniques. The activity results show the high importance of an optimized SiO₂-TiO₂ ratio to reach a high reactant conversion and formaldehyde yield. The characteristics of mixed oxides ensure a better dispersion of the active phase on the support and in this way increase the activity of the catalysts. The addition of vanadium pentoxide on the support lowered the optimal temperature of the reaction significantly. Increasing the vanadia loading from 1.5% to 2.5% did not result in higher formaldehyde concentration. Over the 1.5%V₂O₅/SiO₂ + 30%TiO₂ catalyst, the optimal selectivity was reached at 415 °C when the maximum formaldehyde concentration was ~1000 ppm

Activity, selectivity, and stability of vanadium catalysts in formaldehyde production from emissionsof volatile organic compounds

Abstract In this study, activity, selectivity and stability of vanadium catalysts supported on zirconia, hafnia, and alumina were examined in the oxidation of methanethiol and methanol to formaldehyde. The 3 wt-% vanadia–alumina catalyst with low VOx surface density showed the highest activity in the formaldehyde production. However, during the stability test, this catalyst deactivated due to the change in the oxidation state of vanadium from V5+ to V4+, decrease the amount of surface vanadium species and the formation of sulphates on the material surface. Zirconia and hafnia supported catalysts with high VOx surface density demonstrated better stability in the reaction conditions, but their activity in the formaldehyde production was lower. One reason for the lower activity might be the formation of metal-mixed oxide phases between vanadia and the support, which could also explain the decreased sulphur deposition on zirconia and hafnia after vanadium impregnation