Phenol Hydroxylation over Cu-Containing LDHs and Their Calcined Forms: Profound Cobivalent Metal Influence

Abstract

Copper containing layered double hydroxides (LDHs) with less than 1 atom % Cu along with different cobivalent ions such as magnesium, zinc, nickel or cobalt at (Cu+M(II))/Al atomic ratio 3.0 were synthesized. Calcination of these materials offered mixed metal oxides (refereed here as CLDHs) without any discrete copper oxide phase as confirmed by PXRD and STEM analysis. Hydroxylation of phenol to catechol (CAT) and hydroquinone (HQ) was carried out over both as-synthesized and calcined materials. Among the cobivalent ions, zinc containing samples both in the as-synthesized and calcined forms showed very high activity while cobalt showed the minimum. Variation of copper content for CuZnAl ternary system (0.009 atom % to 0.056 atom %) showed a maximum activity for the sample with 0.038 atom % (CuZnAl-5-CLDH). High activity was attributed to better dispersion of isolated copper species as inferred through TPR measurements. Highly active CuZnAl-5-CLDH can be reused up to three cycles without any significant change in the activity. No significant variation in the conversion was noted when the reaction was scaled up to 200 times over CuZnAl-5-CLDH renders the promise of exploring it to the next level.

Copper Hydroxide Ethanedisulfonate: A Cationic Inorganic Layered Material for High‐Capacity Anion Exchange

“…Intensity data were collected on a D8 goniostat equipped with a Bruker APEXII CCD detector. [Cu 4 (11) 3 ; Z = 4; T = 150(2) K; m(synchrotron) = 6.857 mm À1 ; d calcd = 2.967 g cm À3 ; 7481 reflections collected; 1274 unique (R int = 0.0739); R 1 = 0.0394, wR 2 = 0.1088 for 1022 data with I > 2s(I) and R 1 = 0.0483, wR 2 = 0.1145 for all 1274 data. The data were corrected for absorption and beam corrections based on the multi-scan technique as implemented in SADABS.…”

“…[8,9] Copper-containing LDHs with a second transition or main-group metal are difficult to synthesize but have been shown to catalyze benzene oxidation. [10,11] Also known as hydrotalcites, LDHs are considered plausible alternatives to resins and can exchange many inorganic and organic anions reversibly. Their selectivity towards toxic anions over carbonate and other interfering anions, however, limits adsorption capacities and thus potential application in water purification.…”

The impact of the copper source on the synthesis of meso-structured CuTUD-1: a promising catalyst for phenol hydroxylation

“…As expected, increasing the reaction temperature, an increase in the phenol conversion was noticed whereas a maximum catechol selectivity of about 85% was achieved at 60 °C. At a higher temperature (80 °C), visible tar like products were detected in the reaction which is due to the deep oxidation of 65 benzoquinone and their yield was estimated to be about 5% by weight 17,21 . Similar observations were also reported for metallic Cu nanoparticles catalyzed phenol hydroxylation 38 .…”

A New Fe(III)/MOF‐5(Ni) Catalyst for Highly Selective Synthesis of Catechol from Phenol and Hydrogen Peroxide

“…However, the hydroquinone and some undesirable large molecule benzoquinone may be formed with the production of catechol in the direct oxidation of phenol with hydrogen peroxide . There are a lot of effort to increase the phenol conversion and dihydroxybenzene selectivity . However, there is little report on improving catechol selectivity alone.…”