Titania-Carbon Nitride Interfaces in Gold-Catalyzed CO Oxidation

Abstract

Gold-catalyzed CO oxidation is a reaction of both practical and fundamental interest. In particular, rate-determining oxygen activation pathways have attracted a lot of attention. They have been found to depend on the surface chemistry of the catalyst support, titania providing the most active catalysts and carbon nitride leading to inactive catalysts. Here, we show that C3N4-TiO2 composites with rather similar surface chemistries can be engineered by using titania nanotubes as hard templates and by performing the polycondensation of melamine and dicyandiamide in air and in ammonia. By varying the C3N4 content from 2 to 75 wt %, the mesoporosity can be tuned from 8 to 40 nm. A systematic study of CO oxidation turnover numbers in the absence and in the presence of hydrogen over the composites loaded with well-calibrated 2–4 nm gold nanoparticles clearly shows that (1) the chemical composition of the support surface has much less impact on PROX (preferential oxidation of CO in excess hydrogen) than on dry CO oxidation, (2) NH2-terminated supports are as active as OH-terminated supports in PROX, (3) hydrogen/water-mediated CO oxidation pathways are active on C3N4-based Au catalysts, and (4) PROX activity requires a rather large porosity (40 nm), which suggests the involvement of much larger intermediates than the usually postulated peroxo-type species.

Tuning CH4 Productivity from Visible Light‐Driven Gas‐Phase CO2 Photocatalytic Reduction on Doped g‐C3N4/TiO2 Heterojunctions

“…One can mention that this sintering effect of TiO 2 crystallites is hindered within the composite materials during the synthesis and the formation of g‐C 3 N 4 nanosheets upon polycondensation at 550 °C, confirming strong interactions between both semiconductors even at those low graphitic carbon nitride contents, as previously observed. [ 40 ] As a result of the minor g‐C 3 N 4 content (max. 0.72 wt%), XRD patterns showed no obvious diffraction peak (Figure S2, Supporting Information) attributable to crystallized g‐C 3 N 4 .…”

One-pot Synthesis of a Visible-light Responsive Carbon Nitride/TiO2 Heterointerface Material for Photoelectrocatalytic Applications

“…However, TiO2 calcined sample at 550 °C had an anatase crystallite size significantly higher 24.4±0.2 nm, suggesting that calcination temperature has an immediate increase in crystallinity [75] , in agreement with reported studies. [76] N2 isotherms (Fig. S15a) of all samples exhibit type-IV isotherm and type-H4 hysteresis loop, ascribed for mesopores and slit-like pores.…”

The role of the gold–platinum interface in AuPt/TiO2-catalyzed plasmon-induced reduction of CO2 with water

“…In these methods, size and structure of the resulting bimetallic NPs are determined by the kinetics of nucleation vs. growth for each metal, thus by the reduction kinetics, which depend on the reducing agent, solvent, temperature and possible presence of surfactant to enhance size control. The most common reductants include sodium borohydride, [25][26][27][28][29][30] sodium citrate, 31 ascorbic acid, [32][33] hydrogen, hydroxylamine, 34 ethanol.…”