Catalytic methylation of phenol on MgO – Surface chemistry and mechanism

Construction of Acid–Base Synergetic Sites on Mg‐bearing BEA Zeolites Triggers the Unexpected Low‐Temperature Alkylation of Phenol

“…No or trace amountso fc resols were detected over b (entry 5, 0%), solid acids like Hb (entry 6, 0.6 %) and gAl 2 O 3 (entry 7, 1.1 %), commercial solid base MgO (entry 8, 0%), or solid acid-base catalyst MgO@gAl 2 O 3 (entry 9, 0.15 %);a lthough they were active in the high-temperature gas-phase methylation reaction. [22,23] These observations suggestt hat neither solid base nor solid acid are effective for the reaction.Instead, methylation requires both acid and base sites. Nonetheless, basicity introduced through impregnation (that is, Mg (im) -b and MgO@gAl 2 O 3 ) almostdamage the activity,d emonstrating that such separated acid and base sites fail to promote the catalysis.…”

“…Similar negative peaks as gAl 2 O 3 are observed for these samples, implyingt hat some methanoli sa dsorbed throughi nteraction with surface hydroxyl groups.A pparent shifting or splitting is observable for the bands around1 350-1500 cm À1 , which are attributable to the CÀHs tretchingv ibration and COH deformation vibration. [22,53] The band at approximately 1250 cm À1 is attributable to OÀHd eformationv ibration perceived from the zeolite catalyst. These observations reflect the deformation of adsorbed methanolo nt hese zeolitesw itht he elongation of CÀOÀH, which causes the activation of adsorbed methanol.…”

“…Among the variousa lkylation reactions, methylation of phenol with methanoli so ne industrially available pathway to produce cresols, important intermediates for manufacturing functional polymers, antioxidants, pharmaceuticals, and agrochemicals. Various catalystsh ave been developed, such as metal oxides, [20][21][22] zeolites, [23][24][25] sulfates, [26] mixed metal oxides, [27][28][29][30] andh ydrotalcites. [31] MCM-22 with different Si/Al has only approximately 20 %s electivityf or the C-alkylation of phenol at low pressure.…”

Microwave-dried α-Fe2O3 as a highly efficient catalyst for ortho-methylation of phenol with methanol

“…Although MgO has high ortho-selectivity for o-cresol nearly 100%, phenol conversion is only 8.2% at the reaction temperature as high as 673 K, and lacks the test of stability [5][6][7][8]. TiO 2 has phenol conversion about 40%, however the selectivity of o-cresol is only 60% [9][10][11][12].…”

Glycothermal Synthesis and Catalytic Properties of Nanosized Zn1−x Co x Al2O4 (x = 0, 0.5, 1.0) Spinels in Phenol Methylation

“…Suitable catalysts for the gas phase methylation of phenol with methanol have been reported in the literature. Catalysts having basic properties such as MgO [18][19][20] or Fe 2 O 3 -based [21][22][23] produce predominantly ring alkylated products with high ortho-selectivity. With the increase in the acidity of catalysts, e.g.…”